Packaged semiconductor devices including backside power rails and methods of forming the same

ABSTRACT

Methods for forming packaged semiconductor devices including backside power rails and packaged semiconductor devices formed by the same are disclosed. In an embodiment, a device includes a first integrated circuit device including a first transistor structure in a first device layer; a front-side interconnect structure on a front-side of the first device layer; and a backside interconnect structure on a backside of the first device layer, the backside interconnect structure including a first dielectric layer on the backside of the first device layer; and a first contact extending through the first dielectric layer to a source/drain region of the first transistor structure; and a second integrated circuit device including a second transistor structure in a second device layer; and a first interconnect structure on the second device layer, the first interconnect structure being bonded to the front-side interconnect structure by dielectric-to-dielectric and metal-to-metal bonds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.63/023,317, filed on May 12, 2020, and entitled “Semiconductor ChipStack with Back Side Power Rail and Method of Forming the Same,” whichpatent application is incorporated herein by reference.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as, for example, personal computers, cell phones, digital cameras,and other electronic equipment. Semiconductor devices are typicallyfabricated by sequentially depositing insulating or dielectric layers,conductive layers, and semiconductor layers of material over asemiconductor substrate, and patterning the various material layersusing lithography to form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. However, asthe minimum features sizes are reduced, additional problems arise thatshould be addressed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates an example of a nanostructure field-effect transistor(nano-FET) in a three-dimensional view, in accordance with someembodiments.

FIGS. 2, 3, 4, 5, 6A, 6B, 6C, 7A, 7B, 7C, 8A, 8B, 8C, 9A, 9B, 9C, 10A,10B, 10C, 11A, 11B, 11C, 11D, 12A, 12B, 12C, 12D, 12E, 13A, 13B, 13C,14A, 14B, 14C, 15A, 15B, 15C, 16A, 16B, 16C, 17A, 17B, 17C, 18A, 18B,18C, 19A, 19B, 19C, 20A, 20B, 20C, 21A, 21B, 21C, 21D, 22A, 22B, 22C,23A, 23B, 23C, 24A, 24B, 24C, 25A, 25B, 25C, 26A, 26B, 26C, 27A, 27B,27C, 28A, 28B, 28C, 29A, 29B, and 29C are cross-sectional views ofintermediate stages in the manufacturing of nano-FETs, in accordancewith some embodiments.

FIGS. 30 through 51 are cross-sectional views of intermediate stages inthe packaging of integrated circuit dies, in accordance with someembodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Various embodiments provide methods for forming packaged semiconductordevices using hybrid bonding and packaged semiconductor devices formedby the same. The packaged semiconductor devices include stackedintegrated circuit (IC) dies, at least one of which includes a backsideinterconnect structure with a backside power rail. The backside powerrail may be connected to a source/drain region of the stacked IC diethrough a backside via. In some embodiments, a front-side interconnectstructure of a first IC die is hybrid bonded to a front-sideinterconnect structure of a second IC die; a front-side interconnectstructure of a first die is hybrid bonded to a backside interconnectstructure of a second die; or a backside interconnect structure of afirst die is hybrid bonded to a backside interconnect structure of asecond die. Forming packaged semiconductor devices having IC dies whichinclude backside power rails allows for the IC dies to be formed withgreater transistor densities, reduces distances between bonded IC dies,and provides for greater flexibility in IC die stacking and packaging.

Some embodiments discussed herein are described in the context of ICdies including nano-FETs. However, various embodiments may be applied toIC dies including other types of transistors (e.g., fin field effecttransistors (FinFETs), planar transistors, or the like) in lieu of or incombination with the nano-FETs.

FIG. 1 illustrates an example of nano-FETs (e.g., nanowire FETs,nanosheet FETs, or the like) in a three-dimensional view, in accordancewith some embodiments. The nano-FETs comprise nanostructures 55 (e.g.,nanosheets, nanowire, or the like) over fins 66 on a substrate 50 (e.g.,a semiconductor substrate), wherein the nanostructures 55 act as channelregions for the nano-FETs. The nanostructure 55 may include p-typenanostructures, n-type nanostructures, or a combination thereof. Shallowtrench isolation (STI) regions 68 are disposed between adjacent fins 66,which may protrude above and from between neighboring STI regions 68.Although the STI regions 68 are described/illustrated as being separatefrom the substrate 50, as used herein, the term “substrate” may refer tothe semiconductor substrate alone or a combination of the semiconductorsubstrate and the STI regions. Additionally, although bottom portions ofthe fins 66 are illustrated as being single, continuous materials withthe substrate 50, the bottom portions of the fins 66 and/or thesubstrate 50 may comprise a single material or a plurality of materials.In this context, the fins 66 refer to the portion extending between theneighboring STI regions 68.

Gate dielectric layers 100 are over top surfaces of the fins 66 andalong top surfaces, sidewalls, and bottom surfaces of the nanostructures55. Gate electrodes 102 are over the gate dielectric layers 100.Epitaxial source/drain regions 92 are disposed on the fins 66 onopposing sides of the gate dielectric layers 100 and the gate electrodes102.

FIG. 1 further illustrates reference cross-sections that are used inlater figures. Cross-section A-A′ is along a longitudinal axis of a gateelectrode 102 and in a direction, for example, perpendicular to thedirection of current flow between the epitaxial source/drain regions 92of a nano-FET. Cross-section B-B′ is parallel to cross-section A-A′ andextends through epitaxial source/drain regions 92 of multiple nano-FETs.Cross-section C-C′ is perpendicular to cross-section A-A′ and isparallel to a longitudinal axis of a fin 66 of the nano-FET and in adirection of, for example, a current flow between the epitaxialsource/drain regions 92 of the nano-FET. Subsequent figures refer tothese reference cross-sections for clarity.

Some embodiments discussed herein are discussed in the context ofnano-FETs formed using a gate-last process. In other embodiments, agate-first process may be used. Also, some embodiments contemplateaspects used in planar devices, such as planar FETs or in finfield-effect transistors (FinFETs).

FIGS. 2 through 29C are cross-sectional views of intermediate stages inthe manufacturing of nano-FETs, in accordance with some embodiments.FIGS. 2 through 5, 6A, 7A, 8A, 9A, 10A, 11A, 12A, 13A, 14A, 15A, 16A,17A, 18A, 19A, 20A, 21A, 22A, 23A, 24A, 25A, 26A, 27A, 28A, and 29Aillustrate reference cross-section A-A′ illustrated in FIG. 1. FIGS. 6B,7B, 8B, 9B, 10B, 11B, 12B, 12D, 13B, 14B, 15B, 16B, 17B, 18B, 19B, 20B,21B, 22B, 23B, 24B, 25B, 26B, 27B, 28B, and 29B illustrate referencecross-section B-B′ illustrated in FIG. 1. FIGS. 7C, 8C, 9C, 10C, 11C,11D, 12C, 12E, 13C, 14C, 15C, 16C, 17C, 18C, 19C, 20C, 21C, 21D, 22C,23C, 24C, 25C, 26C, 27C, 28C, and 29C illustrate reference cross-sectionC-C′ illustrated in FIG. 1. FIGS. 30 through 51 are cross-sectionalviews of intermediate stages in the packaging of IC dies, in accordancewith some embodiments. FIGS. 30 through 51 illustrate referencecross-section C-C′ illustrated in FIG. 1.

In FIG. 2, a substrate 50 is provided. The substrate 50 may be asemiconductor substrate, such as a bulk semiconductor, asemiconductor-on-insulator (SOI) substrate, or the like, which may bedoped (e.g., with a p-type or an n-type dopant) or undoped. Thesubstrate 50 may be a wafer, such as a silicon wafer. Generally, an SOIsubstrate is a layer of a semiconductor material formed on an insulatorlayer. The insulator layer may be, for example, a buried oxide (BOX)layer, a silicon oxide layer, or the like. The insulator layer isprovided on a substrate, typically a silicon or glass substrate. Othersubstrates, such as a multi-layered or gradient substrate may also beused. In some embodiments, the semiconductor material of the substrate50 may include silicon; germanium; a compound semiconductor includingsilicon carbide, gallium arsenide, gallium phosphide, indium phosphide,indium arsenide, and/or indium antimonide; an alloy semiconductorincluding silicon-germanium, gallium arsenide phosphide, aluminum indiumarsenide, aluminum gallium arsenide, gallium indium arsenide, galliumindium phosphide, and/or gallium indium arsenide phosphide; orcombinations thereof.

The substrate 50 has an n-type region 50N and a p-type region 50P. Then-type region 50N can be for forming n-type devices, such as NMOStransistors, e.g., n-type nano-FETs, and the p-type region 50P can befor forming p-type devices, such as PMOS transistors, e.g., p-typenano-FETs. The n-type region 50N may be physically separated from thep-type region 50P (as illustrated by divider 20), and any number ofdevice features (e.g., other active devices, doped regions, isolationstructures, etc.) may be disposed between the n-type region 50N and thep-type region 50P. Although one n-type region 50N and one p-type region50P are illustrated, any number of n-type regions 50N and p-type regions50P may be provided.

Further in FIG. 2, a multi-layer stack 64 is formed over the substrate50. The multi-layer stack 64 includes alternating layers of firstsemiconductor layers 51A-51C (collectively referred to as firstsemiconductor layers 51) and second semiconductor layers 53A-53C(collectively referred to as second semiconductor layers 53). Forpurposes of illustration and as discussed in greater detail below, thefirst semiconductor layers 51 will be removed and the secondsemiconductor layers 53 will be patterned to form channel regions ofnano-FETs in the n-type region 50N and the p-type region 50P. However,in some embodiments the first semiconductor layers 51 may be removed andthe second semiconductor layers 53 may be patterned to form channelregions of nano-FETs in the n-type region 50N, and the secondsemiconductor layers 53 may be removed and the first semiconductorlayers 51 may be patterned to form channel regions of nano-FETs in thep-type region 50P. In some embodiments the second semiconductor layers53 may be removed and the first semiconductor layers 51 may be patternedto form channel regions of nano-FETs in the n-type region 50N, and thefirst semiconductor layers 51 may be removed and the secondsemiconductor layers 53 may be patterned to form channel regions ofnano-FETs in the p-type region 50P. In some embodiments, the secondsemiconductor layers 53 may be removed and the first semiconductorlayers 51 may be patterned to form channel regions of nano-FETs in boththe n-type region 50N and the p-type region 50P.

The multi-layer stack 64 is illustrated as including three layers ofeach of the first semiconductor layers 51 and the second semiconductorlayers 53 for illustrative purposes. In some embodiments, themulti-layer stack 64 may include any number of the first semiconductorlayers 51 and the second semiconductor layers 53. Each of the layers ofthe multi-layer stack 64 may be epitaxially grown using a process suchas chemical vapor deposition (CVD), atomic layer deposition (ALD), vaporphase epitaxy (VPE), molecular beam epitaxy (MBE), or the like. Invarious embodiments, the first semiconductor layers 51 may be formed ofa first semiconductor material suitable for p-type nano-FETs, such assilicon germanium or the like, and the second semiconductor layers 53may be formed of a second semiconductor material suitable for n-typenano-FETs, such as silicon, silicon carbon, or the like. The multi-layerstack 64 is illustrated as having a bottommost semiconductor layersuitable for p-type nano-FETs for illustrative purposes. In someembodiments, multi-layer stack 64 may be formed such that the bottommostlayer is a semiconductor layer suitable for n-type nano-FETs.

The first semiconductor materials and the second semiconductor materialsmay be materials having a high etch selectivity to one another. As such,the first semiconductor layers 51 of the first semiconductor materialmay be removed without significantly removing the second semiconductorlayers 53 of the second semiconductor material thereby allowing thesecond semiconductor layers 53 to be patterned to form channel regionsof nano-FETs. Similarly, in embodiments in which the secondsemiconductor layers 53 are removed and the first semiconductor layers51 are patterned to form channel regions, the second semiconductorlayers 53 of the second semiconductor material may be removed withoutsignificantly removing the first semiconductor layers 51 of the firstsemiconductor material, thereby allowing the first semiconductor layers51 to be patterned to form channel regions of nano-FETs.

Referring now to FIG. 3, fins 66 are formed in the substrate 50 andnanostructures 55 are formed in the multi-layer stack 64, in accordancewith some embodiments. In some embodiments, the nanostructures 55 andthe fins 66 may be formed in the multi-layer stack 64 and the substrate50, respectively, by etching trenches in the multi-layer stack 64 andthe substrate 50. The etching may be any acceptable etch process, suchas a reactive ion etch (RIE), neutral beam etch (NBE), the like, or acombination thereof. The etching may be anisotropic. Forming thenanostructures 55 by etching the multi-layer stack 64 may further definefirst nanostructures 52A-52C (collectively referred to as the firstnanostructures 52) from the first semiconductor layers 51 and definesecond nano structures 54A-54C (collectively referred to as the secondnanostructures 54) from the second semiconductor layers 53. The firstnanostructures 52 and the second nanostructures 54 may be collectivelyreferred to as nanostructures 55.

The fins 66 and the nanostructures 55 may be patterned by any suitablemethod. For example, the fins 66 and the nanostructures 55 may bepatterned using one or more photolithography processes, includingdouble-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thefins 66.

FIG. 3 illustrates the fins 66 in the n-type region 50N and the p-typeregion 50P as having substantially equal widths for illustrativepurposes. In some embodiments, widths of the fins 66 in the n-typeregion 50N may be greater or thinner than the fins 66 in the p-typeregion 50P. Further, while each of the fins 66 and the nanostructures 55are illustrated as having a consistent width throughout, in otherembodiments, the fins 66 and/or the nanostructures 55 may have taperedsidewalls such that a width of each of the fins 66 and/or thenanostructures 55 continuously increases in a direction towards thesubstrate 50. In such embodiments, each of the nanostructures 55 mayhave a different width and be trapezoidal in shape.

In FIG. 4, shallow trench isolation (STI) regions 68 are formed adjacentthe fins 66. The STI regions 68 may be formed by depositing aninsulation material over the substrate 50, the fins 66, andnanostructures 55, and between adjacent fins 66. The insulation materialmay be an oxide, such as silicon oxide, a nitride, the like, or acombination thereof, and may be formed by high-density plasma CVD(HDP-CVD), flowable CVD (FCVD), the like, or a combination thereof.Other insulation materials formed by any acceptable process may be used.In the illustrated embodiment, the insulation material is silicon oxideformed by an FCVD process. An anneal process may be performed once theinsulation material is formed. In an embodiment, the insulation materialis formed such that excess insulation material covers the nanostructures55. Although the insulation material is illustrated as a single layer,some embodiments may utilize multiple layers. For example, in someembodiments a liner (not separately illustrated) may first be formedalong a surface of the substrate 50, the fins 66, and the nanostructures55. Thereafter, a fill material, such as those discussed above may beformed over the liner.

A removal process is then applied to the insulation material to removeexcess insulation material over the nanostructures 55. In someembodiments, a planarization process such as a chemical mechanicalpolish (CMP), an etch-back process, combinations thereof, or the likemay be utilized. The planarization process exposes the nanostructures 55such that top surfaces of the nanostructures 55 and the insulationmaterial are level after the planarization process is complete.

The insulation material is then recessed to form the STI regions 68. Theinsulation material is recessed such that upper portions of fins 66 inthe n-type region 50N and the p-type region 50P protrude from betweenneighboring STI regions 68. Further, the top surfaces of the STI regions68 may have a flat surface as illustrated, a convex surface, a concavesurface (such as dishing), or a combination thereof. The top surfaces ofthe STI regions 68 may be formed flat, convex, and/or concave by anappropriate etch. The STI regions 68 may be recessed using an acceptableetching process, such as one that is selective to the material of theinsulation material (e.g., etches the material of the insulationmaterial at a faster rate than the material of the fins 66 and thenanostructures 55). For example, an oxide removal using, for example,dilute hydrofluoric (dHF) acid may be used.

The process described above with respect to FIGS. 2 through 4 is justone example of how the fins 66 and the nanostructures 55 may be formed.In some embodiments, the fins 66 and/or the nanostructures 55 may beformed using a mask and an epitaxial growth process. For example, adielectric layer can be formed over a top surface of the substrate 50,and trenches can be etched through the dielectric layer to expose theunderlying substrate 50. Epitaxial structures can be epitaxially grownin the trenches, and the dielectric layer can be recessed such that theepitaxial structures protrude from the dielectric layer to form the fins66 and/or the nanostructures 55. The epitaxial structures may comprisethe alternating semiconductor materials discussed above, such as thefirst semiconductor materials and the second semiconductor materials. Insome embodiments where epitaxial structures are epitaxially grown, theepitaxially grown materials may be in situ doped during growth, whichmay obviate prior and/or subsequent implantations, although in situ andimplantation doping may be used together.

Additionally, the first semiconductor layers 51 (and resulting firstnanostructures 52) and the second semiconductor layers 53 (and resultingsecond nanostructures 54) are illustrated and discussed herein ascomprising the same materials in the p-type region 50P and the n-typeregion 50N for illustrative purposes only. As such, in some embodimentsone or both of the first semiconductor layers 51 and the secondsemiconductor layers 53 may be different materials or formed in adifferent order in the p-type region 50P and the n-type region 50N.

Further in FIG. 4, appropriate wells (not separately illustrated) may beformed in the fins 66, the nanostructures 55, and/or the STI regions 68.In embodiments with different well types, different implant steps forthe n-type region 50N and the p-type region 50P may be achieved using aphotoresist or other masks (not separately illustrated). For example, aphotoresist may be formed over the fins 66 and the STI regions 68 in then-type region 50N and the p-type region 50P. The photoresist ispatterned to expose the p-type region 50P. The photoresist can be formedby using a spin-on technique and can be patterned using acceptablephotolithography techniques. Once the photoresist is patterned, ann-type impurity implant is performed in the p-type region 50P, and thephotoresist may act as a mask to substantially prevent n-type impuritiesfrom being implanted into the n-type region 50N. The n-type impuritiesmay be phosphorus, arsenic, antimony, or the like implanted in theregion to a concentration in a range from about 10¹³ atoms/cm³ to about10¹⁴ atoms/cm³. After the implant, the photoresist is removed, such asby an acceptable ashing process.

Following or prior to the implanting of the p-type region 50P, aphotoresist or other masks (not separately illustrated) is formed overthe fins 66, the nanostructures 55, and the STI regions 68 in the p-typeregion 50P and the n-type region 50N. The photoresist is patterned toexpose the n-type region 50N. The photoresist can be formed by using aspin-on technique and can be patterned using acceptable photolithographytechniques. Once the photoresist is patterned, a p-type impurity implantmay be performed in the n-type region 50N, and the photoresist may actas a mask to substantially prevent p-type impurities from beingimplanted into the p-type region 50P. The p-type impurities may beboron, boron fluoride, indium, or the like implanted in the region to aconcentration in a range from about 10¹³ atoms/cm³ to about 10¹⁴atoms/cm³. After the implant, the photoresist may be removed, such as byan acceptable ashing process.

After the implants of the n-type region 50N and the p-type region 50P,an anneal may be performed to repair implant damage and to activate thep-type and/or n-type impurities that were implanted. In someembodiments, the grown materials of epitaxial fins may be in situ dopedduring growth, which may obviate the implantations, although in situ andimplantation doping may be used together.

In FIG. 5, a dummy dielectric layer 70 is formed on the fins 66 and/orthe nanostructures 55. The dummy dielectric layer 70 may be, forexample, silicon oxide, silicon nitride, a combination thereof, or thelike, and may be deposited or thermally grown according to acceptabletechniques. A dummy gate layer 72 is formed over the dummy dielectriclayer 70, and a mask layer 74 is formed over the dummy gate layer 72.The dummy gate layer 72 may be deposited over the dummy dielectric layer70 and then planarized, such as by a CMP. The mask layer 74 may bedeposited over the dummy gate layer 72. The dummy gate layer 72 may be aconductive or non-conductive material and may be selected from a groupincluding amorphous silicon, polycrystalline-silicon (polysilicon),poly-crystalline silicon-germanium (poly-SiGe), metallic nitrides,metallic silicides, metallic oxides, and metals. The dummy gate layer 72may be deposited by physical vapor deposition (PVD), CVD, sputterdeposition, or other techniques for depositing the selected material.The dummy gate layer 72 may be made of other materials that have a highetching selectivity from the etching of isolation regions. The masklayer 74 may include, for example, silicon nitride, silicon oxynitride,or the like. In this example, a single dummy gate layer 72 and a singlemask layer 74 are formed across the n-type region 50N and the p-typeregion 50P. It is noted that the dummy dielectric layer 70 is showncovering only the fins 66 and the nanostructures 55 for illustrativepurposes only. In some embodiments, the dummy dielectric layer 70 may bedeposited such that the dummy dielectric layer 70 covers the STI regions68, such that the dummy dielectric layer 70 extends between the dummygate layer 72 and the STI regions 68.

FIGS. 6A through 18C illustrate various additional steps in themanufacturing of embodiment devices. FIGS. 6A through 18C illustratefeatures in either the n-type region 50N or the p-type region 50P. InFIGS. 6A through 6C, the mask layer 74 (see FIG. 5) may be patternedusing acceptable photolithography and etching techniques to form masks78. The pattern of the masks 78 then may be transferred to the dummygate layer 72 and to the dummy dielectric layer 70 to form dummy gates76 and dummy gate dielectrics 71, respectively. The dummy gates 76 coverrespective channel regions of the fins 66. The pattern of the masks 78may be used to physically separate each of the dummy gates 76 fromadjacent dummy gates 76. The dummy gates 76 may also have a lengthwisedirection substantially perpendicular to the lengthwise direction ofrespective fins 66.

In FIGS. 7A through 7C, a first spacer layer 80 and a second spacerlayer 82 are formed over the structures illustrated in FIGS. 6A through6C. The first spacer layer 80 and the second spacer layer 82 will besubsequently patterned to act as spacers for forming self-alignedsource/drain regions. In FIGS. 7A through 7C, the first spacer layer 80is formed on top surfaces of the STI regions 68; top surfaces andsidewalls of the fins 66, the nanostructures 55, and the masks 78; andsidewalls of the dummy gates 76 and the dummy gate dielectric 71. Thesecond spacer layer 82 is deposited over the first spacer layer 80. Thefirst spacer layer 80 may be formed of silicon oxide, silicon nitride,silicon oxynitride, or the like, using techniques such as thermaloxidation or deposited by CVD, ALD, or the like. The second spacer layer82 may be formed of a material having a different etch rate than thematerial of the first spacer layer 80, such as silicon oxide, siliconnitride, silicon oxynitride, or the like, and may be deposited by CVD,ALD, or the like.

After the first spacer layer 80 is formed and prior to forming thesecond spacer layer 82, implants for lightly doped source/drain (LDD)regions (not separately illustrated) may be performed. In embodimentswith different device types, similar to the implants discussed above inFIG. 4, a mask, such as a photoresist, may be formed over the n-typeregion 50N, while exposing the p-type region 50P, and appropriate type(e.g., p-type) impurities may be implanted into the exposed fins 66 andnanostructures 55 in the p-type region 50P. The mask may then beremoved. Subsequently, a mask, such as a photoresist, may be formed overthe p-type region 50P while exposing the n-type region 50N, andappropriate type impurities (e.g., n-type) may be implanted into theexposed fins 66 and nanostructures 55 in the n-type region 50N. The maskmay then be removed. The n-type impurities may be the any of the n-typeimpurities previously discussed, and the p-type impurities may be theany of the p-type impurities previously discussed. The lightly dopedsource/drain regions may have a concentration of impurities in a rangefrom about 1×10¹⁵ atoms/cm³ to about 1×10¹⁹ atoms/cm³. An anneal may beused to repair implant damage and to activate the implanted impurities.

In FIGS. 8A through 8C, the first spacer layer 80 and the second spacerlayer 82 are etched to form first spacers 81 and second spacers 83. Aswill be discussed in greater detail below, the first spacers 81 and thesecond spacers 83 act to self-align subsequently formed source/drainregions, as well as to protect sidewalls of the fins 66 and/ornanostructure 55 during subsequent processing. The first spacer layer 80and the second spacer layer 82 may be etched using a suitable etchingprocess, such as an isotropic etching process (e.g., a wet etchingprocess), an anisotropic etching process (e.g., a dry etching process),or the like. In some embodiments, the material of the second spacerlayer 82 has a different etch rate than the material of the first spacerlayer 80, such that the first spacer layer 80 may act as an etch stoplayer when patterning the second spacer layer 82 and such that thesecond spacer layer 82 may act as a mask when patterning the firstspacer layer 80. For example, the second spacer layer 82 may be etchedusing an anisotropic etch process wherein the first spacer layer 80 actsas an etch stop layer, wherein remaining portions of the second spacerlayer 82 form second spacers 83 as illustrated in FIG. 8B. Thereafter,the second spacers 83 acts as a mask while etching exposed portions ofthe first spacer layer 80, thereby forming first spacers 81 asillustrated in FIGS. 8B and 8C.

As illustrated in FIG. 8B, the first spacers 81 and the second spacers83 are disposed on sidewalls of the fins 66 and/or nanostructures 55. Asillustrated in FIG. 8C, in some embodiments, the second spacer layer 82may be removed from over the first spacer layer 80 adjacent the masks78, the dummy gates 76, and the dummy gate dielectrics 71, and the firstspacers 81 are disposed on sidewalls of the masks 78, the dummy gates76, and the dummy gate dielectrics 71. In other embodiments, a portionof the second spacer layer 82 may remain over the first spacer layer 80adjacent the masks 78, the dummy gates 76, and the dummy gatedielectrics 71.

It is noted that the above disclosure generally describes a process offorming spacers and LDD regions. Other processes and sequences may beused. For example, fewer or additional spacers may be utilized,different sequence of steps may be utilized (e.g., the first spacers 81may be patterned prior to depositing the second spacer layer 82),additional spacers may be formed and removed, and/or the like.Furthermore, the n-type and p-type devices may be formed using differentstructures and steps.

In FIGS. 9A through 9C, first recesses 86 are formed in the fins 66, thenanostructures 55, and the substrate 50, in accordance with someembodiments. Epitaxial source/drain regions will be subsequently formedin the first recesses 86. The first recesses 86 may extend through thefirst nanostructures 52 and the second nanostructures 54, and into thesubstrate 50. As illustrated in FIG. 9A, top surfaces of the STI regions68 may be level with bottom surfaces of the first recesses 86. Invarious embodiments, the fins 66 may be etched such that bottom surfacesof the first recesses 86 are disposed below the top surfaces of the STIregions 68; or the like. The first recesses 86 may be formed by etchingthe fins 66, the nanostructures 55, and the substrate 50 usinganisotropic etching processes, such as RIE, NBE, or the like. The firstspacers 81, the second spacers 83, and the masks 78 mask portions of thefins 66, the nanostructures 55, and the substrate 50 during the etchingprocesses used to form the first recesses 86. A single etch process ormultiple etch processes may be used to etch each layer of thenanostructures 55 and/or the fins 66. Timed etch processes may be usedto stop the etching of the first recesses 86 after the first recesses 86reach a desired depth.

In FIGS. 10A through 10C, portions of sidewalls of the layers of themulti-layer stack 64 formed of the first semiconductor materials (e.g.,the first nanostructures 52) exposed by the first recesses 86 are etchedto form sidewall recesses 88. Although sidewalls of the firstnanostructures 52 adjacent the sidewall recesses 88 are illustrated asbeing straight in FIG. 10C, the sidewalls may be concave or convex. Thesidewalls may be etched using isotropic etching processes, such as wetetching or the like. In an embodiment in which the first nanostructures52 include, e.g., SiGe, and the second nanostructures 54 include, e.g.,Si or SiC, a dry etch process with tetramethylammonium hydroxide (TMAH),ammonium hydroxide (NH₄OH), or the like may be used to etch sidewalls ofthe first nanostructures 52.

In FIGS. 11A through 11D, first inner spacers 90 are formed in thesidewall recess 88. The first inner spacers 90 may be formed bydepositing an inner spacer layer (not separately illustrated) over thestructures illustrated in FIGS. 10A through 10C. The first inner spacers90 act as isolation features between subsequently formed source/drainregions and a gate structure. As will be discussed in greater detailbelow, source/drain regions will be formed in the first recesses 86,while the first nanostructures 52 will be replaced with correspondinggate structures.

The inner spacer layer may be deposited by a conformal depositionprocess, such as CVD, ALD, or the like. The inner spacer layer maycomprise a material such as silicon nitride or silicon oxynitride,although any suitable material, such as low-dielectric constant (low-k)materials having a k-value less than about 3.5, may be utilized. Theinner spacer layer may then be anisotropically etched to form the firstinner spacers 90. Although outer sidewalls of the first inner spacers 90are illustrated as being flush with sidewalls of the secondnanostructures 54, the outer sidewalls of the first inner spacers 90 mayextend beyond or be recessed from sidewalls of the second nanostructures54.

Moreover, although the outer sidewalls of the first inner spacers 90 areillustrated as being straight in FIG. 11C, the outer sidewalls of thefirst inner spacers 90 may be concave or convex. As an example, FIG. 11Dillustrates an embodiment in which sidewalls of the first nanostructures52 are concave, outer sidewalls of the first inner spacers 90 areconcave, and the first inner spacers 90 are recessed from sidewalls ofthe second nanostructures 54. The inner spacer layer may be etched by ananisotropic etching process, such as RIE, NBE, or the like. The firstinner spacers 90 may be used to prevent damage to subsequently formedsource/drain regions (such as the epitaxial source/drain regions 92,discussed below with respect to FIGS. 12A through 12E) by subsequentetching processes, such as etching processes used to form gatestructures.

In FIGS. 12A through 12E, epitaxial source/drain regions 92 are formedin the first recesses 86. In some embodiments, the epitaxialsource/drain regions 92 may exert stress on the second nanostructures54, thereby improving performance. As illustrated in FIG. 12C, theepitaxial source/drain regions 92 are formed in the first recesses 86such that each dummy gate 76 is disposed between respective neighboringpairs of the epitaxial source/drain regions 92. In some embodiments, thefirst spacers 81 are used to separate the epitaxial source/drain regions92 from the dummy gates 76 and the first inner spacers 90 are used toseparate the epitaxial source/drain regions 92 from the firstnanostructures 52 by appropriate lateral distances so that the epitaxialsource/drain regions 92 do not short out with subsequently formed gatesof the resulting nano-FETs.

The epitaxial source/drain regions 92 in the n-type region 50N, e.g.,the NMOS region, may be formed by masking the p-type region 50P, e.g.,the PMOS region. Then, the epitaxial source/drain regions 92 areepitaxially grown in the first recesses 86 in the n-type region 50N. Theepitaxial source/drain regions 92 may include any acceptable materialappropriate for n-type nano-FETs. For example, if the secondnanostructures 54 are silicon, the epitaxial source/drain regions 92 mayinclude materials exerting a tensile strain on the second nanostructures54, such as silicon, silicon carbide, phosphorous doped silicon carbide,silicon phosphide, or the like. The epitaxial source/drain regions 92may have surfaces raised from respective upper surfaces of thenanostructures 55 and may have facets.

The epitaxial source/drain regions 92 in the p-type region 50P, e.g.,the PMOS region, may be formed by masking the n-type region 50N, e.g.,the NMOS region. Then, the epitaxial source/drain regions 92 areepitaxially grown in the first recesses 86 in the p-type region 50P. Theepitaxial source/drain regions 92 may include any acceptable materialappropriate for p-type nano-FETs. For example, if the secondnanostructures 54 are silicon, the epitaxial source/drain regions 92 maycomprise materials exerting a compressive strain on the secondnanostructures 54, such as silicon-germanium, boron dopedsilicon-germanium, germanium, germanium tin, or the like. The epitaxialsource/drain regions 92 may have surfaces raised from respective uppersurfaces of the nanostructures 55 and may have facets.

The epitaxial source/drain regions 92, the second nanostructures 54,and/or the substrate 50 may be implanted with dopants to formsource/drain regions, similar to the process previously discussed forforming lightly-doped source/drain regions, followed by an anneal. Thesource/drain regions may have an impurity concentration of between about1×10¹⁹ atoms/cm³ and about 1×10²¹ atoms/cm³. The n-type and/or p-typeimpurities for source/drain regions may be any of the impuritiespreviously discussed. In some embodiments, the epitaxial source/drainregions 92 may be in situ doped during growth.

As a result of the epitaxy processes used to form the epitaxialsource/drain regions 92 in the n-type region 50N and the p-type region50P, upper surfaces of the epitaxial source/drain regions 92 have facetswhich expand laterally outward beyond sidewalls of the nanostructures55. In some embodiments, these facets cause adjacent epitaxialsource/drain regions 92 of a same nano-FET to merge as illustrated byFIG. 12B. In other embodiments, adjacent epitaxial source/drain regions92 remain separated after the epitaxy process is completed asillustrated by FIG. 12D. In the embodiments illustrated in FIGS. 12B and12D, the first spacers 81 may be formed to a top surface of the STIregions 68 thereby blocking the epitaxial growth. In some otherembodiments, the first spacers 81 may cover portions of the sidewalls ofthe nanostructures 55 further blocking the epitaxial growth. In someother embodiments, the spacer etch used to form the first spacers 81 maybe adjusted to remove the spacer material to allow the epitaxially grownregion to extend to the surface of the STI region 58.

The epitaxial source/drain regions 92 may comprise one or moresemiconductor material layers. For example, the epitaxial source/drainregions 92 may comprise a first semiconductor material layer 92A, asecond semiconductor material layer 92B, and a third semiconductormaterial layer 92C. Any number of semiconductor material layers may beused for the epitaxial source/drain regions 92. Each of the firstsemiconductor material layer 92A, the second semiconductor materiallayer 92B, and the third semiconductor material layer 92C may be formedof different semiconductor materials and may be doped to differentdopant concentrations. In some embodiments, the first semiconductormaterial layer 92A may have a dopant concentration less than the secondsemiconductor material layer 92B and greater than the thirdsemiconductor material layer 92C. In embodiments in which the epitaxialsource/drain regions 92 comprise three semiconductor material layers,the first semiconductor material layer 92A may be deposited, the secondsemiconductor material layer 92B may be deposited over the firstsemiconductor material layer 92A, and the third semiconductor materiallayer 92C may be deposited over the second semiconductor material layer92B.

FIG. 12E illustrates an embodiment in which sidewalls of the firstnanostructures 52 are concave, outer sidewalls of the first innerspacers 90 are concave, and the first inner spacers 90 are recessed fromsidewalls of the second nanostructures 54. As illustrated in FIG. 12E,the epitaxial source/drain regions 92 may be formed in contact with thefirst inner spacers 90 and may extend past sidewalls of the secondnanostructures 54.

In FIGS. 13A through 13C, a first interlayer dielectric (ILD) 96 isdeposited over the structure illustrated in FIGS. 12A through 12C. Thefirst ILD 96 may be formed of a dielectric material, and may bedeposited by any suitable method, such as CVD, plasma-enhanced CVD(PECVD), or FCVD. Dielectric materials may include phospho-silicateglass (PSG), boro-silicate glass (BSG), boron-doped phospho-silicateglass (BPSG), undoped silicate glass (USG), or the like. Otherinsulation materials formed by any acceptable process may be used. Insome embodiments, a contact etch stop layer (CESL) 94 is disposedbetween the first ILD 96 and the epitaxial source/drain regions 92, themasks 78, and the first spacers 81. The CESL 94 may comprise adielectric material, such as, silicon nitride, silicon oxide, siliconoxynitride, or the like, having a different etch rate than the materialof the overlying first ILD 96.

In FIGS. 14A through 14C, a planarization process, such as a CMP, may beperformed to level the top surface of the first ILD 96 with the topsurfaces of the dummy gates 76 or the masks 78. The planarizationprocess may also remove the masks 78 on the dummy gates 76, and portionsof the first spacers 81 along sidewalls of the masks 78. After theplanarization process, top surfaces of the dummy gates 76, the firstspacers 81, and the first ILD 96 are level within process variations.Accordingly, the top surfaces of the dummy gates 76 are exposed throughthe first ILD 96. In some embodiments, the masks 78 may remain, in whichcase the planarization process levels the top surface of the first ILD96 with top surface of the masks 78 and the first spacers 81.

In FIGS. 15A through 15C, the dummy gates 76, and the masks 78 ifpresent, are removed in one or more etching steps, so that thirdrecesses 98 are formed. Portions of the dummy gate dielectrics 71 in thethird recesses 98 are also be removed. In some embodiments, the dummygates 76 and the dummy gate dielectrics 71 are removed by an anisotropicdry etch process. For example, the etching process may include a dryetch process using reaction gas(es) that selectively etch the dummygates 76 at a faster rate than the first ILD 96 or the first spacers 81.Each of the third recess 98 exposes and/or overlies portions ofnanostructures 55, which act as channel regions in subsequentlycompleted nano-FETs. Portions of the nanostructures 55 which act as thechannel regions are disposed between neighboring pairs of the epitaxialsource/drain regions 92. During the removal, the dummy gate dielectrics71 may be used as etch stop layers when the dummy gates 76 are etched.The dummy gate dielectrics 71 may then be removed after the removal ofthe dummy gates 76.

In FIGS. 16A through 16C, the first nanostructures 52 are removedextending the third recesses 98. The first nanostructures 52 may beremoved by performing an isotropic etching process such as wet etchingor the like using etchants which are selective to the materials of thefirst nanostructures 52, while the second nanostructures 54, thesubstrate 50, the STI regions 58 remain relatively unetched as comparedto the first nanostructures 52. In embodiments in which the firstnanostructures 52 include, e.g., SiGe, and the second nanostructures54A-54C include, e.g., Si or SiC, tetramethylammonium hydroxide (TMAH),ammonium hydroxide (NH₄OH), or the like may be used to remove the firstnanostructures 52.

In FIGS. 17A through 17C, gate dielectric layers 100 and gate electrodes102 are formed for replacement gates. The gate dielectric layers 100 aredeposited conformally in the third recesses 98. The gate dielectriclayers 100 may be formed on top surfaces and sidewalls of the substrate50 and on top surfaces, sidewalls, and bottom surfaces of the secondnanostructures 54. The gate dielectric layers 100 may also be depositedon top surfaces of the first ILD 96, the CESL 94, the first spacers 81,and the STI regions 68 and on sidewalls of the first spacers 81 and thefirst inner spacers 90.

In accordance with some embodiments, the gate dielectric layers 100comprise one or more dielectric layers, such as an oxide, a metal oxide,the like, or combinations thereof. For example, in some embodiments, thegate dielectrics may comprise a silicon oxide layer and a metal oxidelayer over the silicon oxide layer. In some embodiments, the gatedielectric layers 100 include a high-k dielectric material, and in theseembodiments, the gate dielectric layers 100 may have a k value greaterthan about 7.0, and may include a metal oxide or a silicate of hafnium,aluminum, zirconium, lanthanum, manganese, barium, titanium, lead, andcombinations thereof. The structure of the gate dielectric layers 100may be the same or different in the n-type region 50N and the p-typeregion 50P. The formation methods of the gate dielectric layers 100 mayinclude molecular-beam deposition (MBD), ALD, PECVD, and the like.

The gate electrodes 102 are deposited over the gate dielectric layers100, respectively, and fill the remaining portions of the third recesses98. The gate electrodes 102 may include a metal-containing material suchas titanium nitride, titanium oxide, tantalum nitride, tantalum carbide,cobalt, ruthenium, aluminum, tungsten, combinations thereof, ormulti-layers thereof. For example, although single layer gate electrodes102 are illustrated in FIGS. 17A and 17C, the gate electrodes 102 maycomprise any number of liner layers, any number of work function tuninglayers, and a fill material. Any combination of the layers which make upthe gate electrodes 102 may be deposited between adjacent ones of thesecond nanostructures 54 and between the second nanostructure 54A andthe substrate 50.

The formation of the gate dielectric layers 100 in the n-type region 50Nand the p-type region 50P may occur simultaneously such that the gatedielectric layers 100 in each region are formed from the same materials,and the formation of the gate electrodes 102 may occur simultaneouslysuch that the gate electrodes 102 in each region are formed from thesame materials. In some embodiments, the gate dielectric layers 100 ineach region may be formed by distinct processes, such that the gatedielectric layers 100 may be different materials and/or have a differentnumber of layers, and/or the gate electrodes 102 in each region may beformed by distinct processes, such that the gate electrodes 102 may bedifferent materials and/or have a different number of layers. Variousmasking steps may be used to mask and expose appropriate regions whenusing distinct processes.

After the filling of the third recesses 98, a planarization process,such as a CMP, may be performed to remove the excess portions of thegate dielectric layers 100 and the material of the gate electrodes 102,which excess portions are over the top surface of the first ILD 96. Theremaining portions of material of the gate electrodes 102 and the gatedielectric layers 100 thus form replacement gate structures of theresulting nano-FETs. The gate electrodes 102 and the gate dielectriclayers 100 may be collectively referred to as “gate structures.”

In FIGS. 18A through 18C, the gate structures (including the gatedielectric layers 100 and the corresponding overlying gate electrodes102) are recessed, so that recess are formed directly over the gatestructures and between opposing portions of first spacers 81. Gate masks104 comprising one or more layers of dielectric material, such assilicon nitride, silicon oxynitride, or the like, are filled in therecesses, followed by a planarization process to remove excess portionsof the dielectric material extending over the first ILD 96. Subsequentlyformed gate contacts (such as the gate contacts 114, discussed belowwith respect to FIGS. 20A through 20C) penetrate through the gate masks104 to contact the top surfaces of the recessed gate electrodes 102.

As further illustrated by FIGS. 18A through 18C, a second ILD 106 isdeposited over the first ILD 96 and over the gate masks 104. In someembodiments, the second ILD 106 is a flowable film formed by FCVD. Insome embodiments, the second ILD 106 is formed of a dielectric materialsuch as PSG, BSG, BPSG, USG, or the like, and may be deposited by anysuitable method, such as CVD, PECVD, or the like.

In FIGS. 19A through 19C, the second ILD 106, the first ILD 96, the CESL94, and the gate masks 104 are etched to form fourth recesses 108exposing surfaces of the epitaxial source/drain regions 92 and/or thegate structures. The fourth recesses 108 may be formed by etching usingan anisotropic etching process, such as RIE, NBE, or the like. In someembodiments, the fourth recesses 108 may be etched through the secondILD 106 and the first ILD 96 using a first etching process; may beetched through the gate masks 104 using a second etching process; andmay then be etched through the CESL 94 using a third etching process. Amask, such as a photoresist, may be formed and patterned over the secondILD 106 to mask portions of the second ILD 106 from the first etchingprocess and the second etching process. In some embodiments, the etchingprocess may over-etch, and therefore, the fourth recesses 108 extendinto the epitaxial source/drain regions 92 and/or the gate structures,and a bottom of the fourth recesses 108 may be level with (e.g., at asame level, or having a same distance from the substrate 50), or lowerthan (e.g., closer to the substrate 50) the epitaxial source/drainregions 92 and/or the gate structures. Although FIG. 19C illustrates thefourth recesses 108 as exposing the epitaxial source/drain regions 92and the gate structures in a same cross-section, in various embodiments,the epitaxial source/drain regions 92 and the gate structures may beexposed in different cross-sections, thereby reducing the risk ofshorting subsequently formed contacts.

After the fourth recesses 108 are formed, first silicide regions 110 areformed over the epitaxial source/drain regions 92. In some embodiments,the first silicide regions 110 are formed by first depositing a metal(not separately illustrated) capable of reacting with the semiconductormaterials of the underlying epitaxial source/drain regions 92 (e.g.,silicon, silicon germanium, germanium) to form silicide or germanideregions, such as nickel, cobalt, titanium, tantalum, platinum, tungsten,other noble metals, other refractory metals, rare earth metals or theiralloys, over the exposed portions of the epitaxial source/drain regions92, then performing a thermal anneal process to form the first silicideregions 110. The un-reacted portions of the deposited metal are thenremoved, e.g., by an etching process. Although the first silicideregions 110 are referred to as silicide regions, the first silicideregions 110 may also be germanide regions, or silicon germanide regions(e.g., regions comprising silicide and germanide). In an embodiment, thefirst silicide regions 110 comprise TiSi and have thicknesses rangingfrom about 2 nm to about 10 nm.

In FIGS. 20A through 20C, source/drain contacts 112 and gate contacts114 (also referred to as contact plugs) are formed in the fourthrecesses 108. The source/drain contacts 112 and the gate contacts 114may each comprise one or more layers, such as barrier layers, diffusionlayers, and fill materials. For example, in some embodiments, thesource/drain contacts 112 and the gate contacts 114 each include abarrier layer and a conductive material, and are each electricallycoupled to an underlying conductive feature (e.g., a gate electrode 102and/or a first silicide region 110). The gate contacts 114 areelectrically coupled to the gate electrodes 102 and the source/draincontacts 112 are electrically coupled to the first silicide regions 110.The barrier layer may include titanium, titanium nitride, tantalum,tantalum nitride, or the like. The conductive material may be copper, acopper alloy, silver, gold, tungsten, cobalt, aluminum, nickel, or thelike. A planarization process, such as a CMP, may be performed to removeexcess material from surfaces of the second ILD 106. The epitaxialsource/drain regions 92, the second nanostructures 54, and the gatestructures (including the gate dielectric layers 100 and the gateelectrodes 102) may collectively be referred to as transistor structures109. The transistor structures 109 may be formed in a device layer, witha first interconnect structure (such as the front-side interconnectstructure 120, discussed below with respect to FIGS. 21A through 21D)being formed over a front-side thereof and a second interconnectstructure (such as the backside interconnect structure 136, discussedbelow with respect to FIGS. 28A through 28C) being formed over abackside thereof. Although the device layer is described as havingnano-FETs, other embodiments may include a device layer having differenttypes of transistors (e.g., planar FETs, finFETs, thin film transistors(TFTs), or the like).

Although FIGS. 20A through 20C illustrate a source/drain contact 112extending to each of the epitaxial source/drain regions 92, thesource/drain contacts 112 may be omitted from certain ones of theepitaxial source/drain regions 92. For example, as explained in greaterdetail below, conductive features (e.g., backside vias or power rails)may be subsequently attached through a backside of one or more of theepitaxial source/drain regions 92. For these particular epitaxialsource/drain regions 92, the source/drain contacts 112 may be omitted ormay be dummy contacts that are not electrically connected to anyoverlying conductive lines (such as the first conductive features 122,discussed below with respect to FIGS. 21A through 21D).

FIGS. 21A through 29C illustrate intermediate steps of formingfront-side interconnect structures and backside interconnect structureson the transistor structures 109. The front-side interconnect structuresand the backside interconnect structures may each comprise conductivefeatures that are electrically connected to the nano-FETs formed on thesubstrate 50. FIGS. 21A, 22A, 23A, 24A, 25A, 26A, 27A, 28A, and 29Aillustrate reference cross-section A-A′ illustrated in FIG. 1. FIGS.21B, 22B, 23B, 24B, 25B, 26B, 27B, 28B, and 29B illustrate referencecross-section B-B′ illustrated in FIG. 1. FIGS. 21C, 21D, 22C, 23C, 24C,25C, 26C, 27C, 28C, and 29C illustrate reference cross-section C-C′illustrated in FIG. 1. The process steps described in FIGS. 21A through29C may be applied to both the n-type region 50N and the p-type region50P. As noted above, a back-side conductive feature (e.g., a backsidevia, a power rail, or the like) may be connected to one or more of theepitaxial source/drain regions 92. As such, the source/drain contacts112 may be optionally omitted from the epitaxial source/drain regions92.

In FIGS. 21A through 21D, a front-side interconnect structure 120 isformed on the second ILD 106. The front-side interconnect structure 120may be referred to as a front-side interconnect structure because it isformed on a front-side of the transistor structures 109 (e.g., a side ofthe transistor structures 109 on which active devices are formed).

The front-side interconnect structure 120 may comprise one or morelayers of first conductive features 122 formed in one or more stackedfirst dielectric layers 124. Each of the stacked first dielectric layers124 may comprise a dielectric material, such as a low-k dielectricmaterial, an extra low-k (ELK) dielectric material, or the like. Thefirst dielectric layers 124 may be deposited using an appropriateprocess, such as, CVD, ALD, PVD, PECVD, or the like.

The first conductive features 122 may comprise conductive lines andconductive vias interconnecting the layers of conductive lines. Theconductive vias may extend through respective ones of the firstdielectric layers 124 to provide vertical connections between layers ofthe conductive lines. The first conductive features 122 may be formedthrough any acceptable process, such as, a damascene process, a dualdamascene process, or the like.

In some embodiments, the first conductive features 122 may be formedusing a damascene process in which a respective first dielectric layer124 is patterned utilizing a combination of photolithography and etchingtechniques to form trenches corresponding to the desired pattern of thefirst conductive features 122. An optional diffusion barrier and/oroptional adhesion layer may be deposited and the trenches may then befilled with a conductive material. Suitable materials for the barrierlayer include titanium, titanium nitride, titanium oxide, tantalum,tantalum nitride, titanium oxide, combinations thereof, or the like, andsuitable materials for the conductive material include copper, silver,gold, tungsten, aluminum, combinations thereof, or the like. In anembodiment, the first conductive features 122 may be formed bydepositing a seed layer of copper or a copper alloy, and filling thetrenches by electroplating. A chemical mechanical planarization (CMP)process or the like may be used to remove excess conductive materialfrom a surface of the respective first dielectric layer 124 and toplanarize surfaces of the first dielectric layer 124 and the firstconductive features 122 for subsequent processing.

FIGS. 21A through 21D illustrate five layers of the first conductivefeatures 122 and the first dielectric layers 124 in the front-sideinterconnect structure 120. However, it should be appreciated that thefront-side interconnect structure 120 may comprise any number of firstconductive features 122 disposed in any number of first dielectriclayers 124. The front-side interconnect structure 120 may beelectrically connected to the gate contacts 114 and the source/draincontacts 112 to form functional circuits. In some embodiments, thefunctional circuits formed by the front-side interconnect structure 120may comprise logic circuits, memory circuits, image sensor circuits, orthe like.

As will be discussed in greater detail below with respect to FIGS. 30through 32 and 42 through 51, the structures illustrated in FIGS. 21Athrough 21C may be diced to form first integrated circuit dies 200A,which may subsequently be used to form packaged semiconductor devices(such as the first packaged semiconductor device 300A, discussed belowwith respect to FIGS. 30 through 32, the fourth packaged semiconductordevice 300D, discussed below with respect to FIGS. 42 through 46, andthe fifth packaged semiconductor device 300E, discussed below withrespect to FIGS. 47 through 51). The dicing process may include sawing,a laser ablation method, an etching process, a combination thereof, orthe like.

FIG. 21D illustrates an embodiment in which the front-side interconnectstructure 120 further includes first conductive lines 118 and a seconddielectric layer 116 formed over the second ILD 106, the source/draincontacts 112, and the gate contacts 114. As illustrated in FIG. 21D, thefirst conductive features 122 and the first dielectric layers 124 may beformed over the first conductive lines 118 and the second dielectriclayer 116. The second dielectric layer 116 may be similar to the firstdielectric layers 124. For example, the second dielectric layer 116 maybe formed of a like material and using a like process as the firstdielectric layers 124.

The first conductive lines 118 are formed in the second dielectric layer116. Forming the first conductive lines 118 may include patterningrecesses in the second dielectric layer 116 using a combination ofphotolithography and etching processes, for example. A pattern of therecesses in the second dielectric layer 116 may correspond to a patternof the first conductive lines 118. The first conductive lines 118 arethen formed by depositing a conductive material in the recesses. In someembodiments, the first conductive lines 118 comprise a metal layer,which may be a single layer or a composite layer comprising a pluralityof sub-layers formed of different materials. In some embodiments, thefirst conductive lines 118 comprise copper, aluminum, cobalt, tungsten,titanium, tantalum, ruthenium, or the like. An optional diffusionbarrier and/or optional adhesion layer may be deposited prior to fillingthe recesses with the conductive material. Suitable materials for thebarrier layer/adhesion layer include titanium, titanium nitride,titanium oxide, tantalum, tantalum nitride, titanium oxide, or the like.The first conductive lines 118 may be formed using, for example, CVD,ALD, PVD, plating or the like. The first conductive lines 118 may beelectrically coupled to the epitaxial source/drain regions 92 throughthe source/drain contacts 112 and the first silicide regions 110 and maybe electrically coupled to the gate electrodes 102 through the gatecontacts 114.

A planarization process (e.g., a CMP, a grinding, an etch-back, or thelike) may be performed to remove excess portions of the first conductivelines 118 formed over the second dielectric layer 116. In someembodiments, the first conductive lines 118 are front-side power rails,which are conductive lines that electrically connect the epitaxialsource/drain regions 92 and/or the gate electrode 102 to a referencevoltage, a supply voltage, or the like.

As will be discussed in greater detail below with respect to FIGS. 30through 36, the structures illustrated in FIG. 21D may be diced to formsecond integrated circuit dies 200B, which may subsequently be used toform packaged semiconductor devices (such as the first packagedsemiconductor device 300A, discussed below with respect to FIGS. 30through 32 and the second packaged semiconductor device 300B, discussedbelow with respect to FIGS. 33 through 36). The dicing process mayinclude sawing, a laser ablation method, an etching process, acombination thereof, or the like.

In FIGS. 22A through 22C, a first carrier substrate 150 is bonded to atop surface of the front-side interconnect structure 120 by a firstbonding layer 152A and a second bonding layer 152B (collectivelyreferred to as a bonding layer 152). The first carrier substrate 150 maybe a glass carrier substrate, a ceramic carrier substrate, a wafer(e.g., a silicon wafer), or the like. The first carrier substrate 150may provide structural support during subsequent processing steps and inthe completed device.

In various embodiments, the first carrier substrate 150 may be bonded tothe front-side interconnect structure 120 using a suitable technique,such as dielectric-to-dielectric bonding, or the like. Thedielectric-to-dielectric bonding may comprise depositing the firstbonding layer 152A on the front-side interconnect structure 120. In someembodiments, the first bonding layer 152A comprises silicon oxide (e.g.,a high-density plasma (HDP) oxide or the like) that is deposited by CVD,ALD, PVD, or the like. The second bonding layer 152B may likewise be anoxide layer that is formed on a surface of the first carrier substrate150 prior to bonding using, for example, CVD, ALD, PVD, thermaloxidation, or the like. Other suitable materials may be used for thefirst bonding layer 152A and the second bonding layer 152B.

The dielectric-to-dielectric bonding process may further includeapplying a surface treatment to one or more of the first bonding layer152A and the second bonding layer 152B. The surface treatment mayinclude a plasma treatment. The plasma treatment may be performed in avacuum environment. After the plasma treatment, the surface treatmentmay further include a cleaning process (e.g., a rinse with deionizedwater or the like) that may be applied to one or more of the bondinglayers 152. The first carrier substrate 150 is then aligned with thefront-side interconnect structure 120 and the two are pressed againsteach other to initiate a pre-bonding of the first carrier substrate 150to the front-side interconnect structure 120. The pre-bonding may beperformed at room temperature (e.g., from about 21° C. to about 25° C.).After the pre-bonding, an annealing process may be applied by, forexample, heating the front-side interconnect structure 120 and the firstcarrier substrate 150 to a temperature of about 170° C.

Further in FIGS. 22A through 22C, after the first carrier substrate 150is bonded to the front-side interconnect structure 120, the device maybe flipped such that a backside of the transistor structures 109 facesupwards. The backside of the transistor structures 109 may refer to aside opposite to the front-side of the transistor structures 109 onwhich the active devices are formed.

In FIGS. 23A through 23C, a thinning process may be applied to thebackside of the substrate 50. The thinning process may comprise aplanarization process (e.g., a mechanical grinding, a CMP, or the like),an etch-back process, a combination thereof, or the like. The thinningprocess may expose surfaces of the epitaxial source/drain regions 92,the gate dielectric layers 100, the fins 66, the first spacers 81, andthe CESL 94 opposite the front-side interconnect structure 120. Portionsof the substrate 50 may remain over the gate structure (e.g., the gateelectrodes 102 and the gate dielectric layers 100) and thenanostructures 55 after the thinning process.

In FIGS. 24A through 24C, a third dielectric layer 126 is deposited onthe backside of the device. The third dielectric layer 126 may bedeposited over the epitaxial source/drain regions 92, remaining portionsof the substrate 50, the gate dielectric layers 100, the fins 66, thefirst spacers 81, and the CESL 94. The third dielectric layer 126 mayphysically contact surfaces of the epitaxial source/drain regions 92,the remaining portions of the substrate 50, the gate dielectric layers100, the fins 66, the first spacers 81, and the CESL 94. The thirddielectric layer 126 may be substantially similar to the second ILD 106described above. For example, the third dielectric layer 126 may beformed of a like material and using a like process as the second ILD106.

In FIGS. 25A through 25C, fifth recesses 128 are patterned in the thirddielectric layer 126. The fifth recesses 128 may be patterned usingprocesses the same as or similar to those used to form the fourthrecesses 108, described above with respect to FIGS. 19A through 19C. Thefifth recesses 128 may expose surfaces of the epitaxial source/drainregions 92. As also illustrated in FIGS. 25B and 25C, second silicideregions 129 are formed on a backside of the epitaxial source/drainregions 92. The second silicide regions 129 may be similar to the firstsilicide regions 110, described above with respect to FIGS. 19A through19C. For example, the second silicide regions 129 may be formed ofmaterials and using processes the same as or similar to those used forthe first silicide regions 110.

In FIGS. 26A through 26C, backside vias 130 are formed in the fifthrecesses 128. The backside vias 130 may extend through the thirddielectric layer 126 and may be electrically coupled to the epitaxialsource/drain regions 92 through the second silicide regions 129. Thebackside vias 130 may be similar to the source/drain contacts 112,described above with respect to FIGS. 20A through 20C. For example, thebackside vias 130 may be formed of materials and using processes thesame as or similar to those used for the source/drain contacts 112.

In FIGS. 27A through 27C, second conductive lines 134 and a fourthdielectric layer 132 are formed over the third dielectric layer 126, theSTI regions 68, and the backside vias 130. The fourth dielectric layer132 may be similar to the third dielectric layer 126. For example, thefourth dielectric layer 132 may be formed of materials and usingprocesses the same as or similar to those used for the second dielectriclayer 125.

The second conductive lines 134 are formed in the fourth dielectriclayer 132. Forming the second conductive lines 134 may includepatterning recesses in the fourth dielectric layer 132 using acombination of photolithography and etching processes, for example. Apattern of the recesses in the fourth dielectric layer 132 maycorrespond to a pattern of the second conductive lines 134. The secondconductive lines 134 are then formed by depositing a conductive materialin the recesses. In some embodiments, the second conductive lines 134comprise a metal layer, which may be a single layer or a composite layercomprising a plurality of sub-layers formed of different materials. Insome embodiments, the second conductive lines 134 comprise copper,aluminum, cobalt, tungsten, titanium, tantalum, ruthenium, or the like.An optional diffusion barrier and/or optional adhesion layer may bedeposited prior to filling the recesses with the conductive material.Suitable materials for the barrier layer/adhesion layer includetitanium, titanium nitride, titanium oxide, tantalum, tantalum nitride,titanium oxide, or the like. The second conductive lines 134 may beformed using, for example, CVD, ALD, PVD, plating or the like. Thesecond conductive lines 134 are electrically coupled to the epitaxialsource/drain regions 92 through the backside vias 130 and the secondsilicide regions 129. A planarization process (e.g., a CMP, a grinding,an etch-back, or the like) may be performed to remove excess portions ofthe second conductive lines 134 formed over the fourth dielectric layer132.

In some embodiments, the second conductive lines 134 are backside powerrails, which are conductive lines that electrically connect theepitaxial source/drain regions 92 to a reference voltage, a supplyvoltage, or the like. By placing power rails on a backside of theresulting semiconductor die rather than on a front-side of thesemiconductor die, advantages may be achieved. For example, a gatedensity of the nano-FETs and/or interconnect density of the front-sideinterconnect structure 120 may be increased. Further, the backside ofthe semiconductor die may accommodate wider power rails, reducingresistance and increasing efficiency of power delivery to the nano-FETs.For example, a width of the second conductive lines 134 may be at leasttwice a width of first level conductive lines (e.g., the firstconductive features 122 and/or the first conductive lines 118) of thefront-side interconnect structure 120.

In FIGS. 28A through 28C, remaining portions of a backside interconnectstructure 136 are formed over the fourth dielectric layer 132 and thesecond conductive lines 134. The backside interconnect structure 136 maybe referred to as a backside interconnect structure because it is formedon a backside of the transistor structures 109 (e.g., a side of thetransistor structures 109 opposite the side of the transistor structure109 on which active devices are formed). The backside interconnectstructure 136 may comprise the third dielectric layer 126, the fourthdielectric layer 132, the backside vias 130, and the second conductivelines 134.

The remaining portions of the backside interconnect structure 136 maycomprise materials and be formed using processes the same as or similarto those used for the front-side interconnect structure 120, discussedabove with respect to FIGS. 21A through 21C. In particular, the backsideinterconnect structure 136 may comprise stacked layers of secondconductive features 140 formed in fifth dielectric layers 138. Thesecond conductive features 140 may include routing lines (e.g., forrouting to and from subsequently formed contact pads and externalconnectors). The second conductive features 140 may further be patternedto include one or more embedded passive devices such as, resistors,capacitors, inductors, or the like. For example, in FIGS. 28A through28C, the second conductive features 140 may comprise ametal-insulator-metal (MIM) inductor. The embedded passive devices maybe integrated with the second conductive lines 134 (e.g., the powerrail) to provide circuits (e.g., power circuits) on the backside of thenano-FETs.

In FIGS. 29A through 29C, a passivation layer 144, UBMs 146, andexternal connectors 148 are formed over the backside interconnectstructure 136. The passivation layer 144 may comprise polymers such asPBO, polyimide, BCB, or the like. Alternatively, the passivation layer144 may include non-organic dielectric materials such as silicon oxide,silicon nitride, silicon carbide, silicon oxynitride, or the like. Thepassivation layer 144 may be deposited by, for example, CVD, PVD, ALD,or the like.

The UBMs 146 are formed through the passivation layer 144 to the secondconductive features 140 in the backside interconnect structure 136 andthe external connectors 148 are formed on the UBMs 146. The UBMs 146 maycomprise one or more layers of copper, nickel, gold, or the like, whichare formed by a plating process, or the like. The external connectors148 (e.g., solder balls) are formed on the UBMs 146. The formation ofthe external connectors 148 may include placing solder balls on exposedportions of the UBMs 146 and reflowing the solder balls. In someembodiments, the formation of the external connectors 148 includesperforming a plating step to form solder regions over the topmost secondconductive features 140 and then reflowing the solder regions. The UBMs146 and the external connectors 148 may be used to provide input/outputconnections to other electrical components, such as, other device dies,redistribution structures, printed circuit boards (PCBs), motherboards,or the like. The UBMs 146 and the external connectors 148 may also bereferred to as backside input/output pads that may provide signal,supply voltage, and/or ground connections to the nano-FETs describedabove.

FIGS. 30 through 51 illustrate intermediate steps of forming packagedsemiconductor devices, which may include nano-FETs formed by theprocesses described above. FIGS. 30 through 51 illustrate referencecross-section C-C′ illustrated in FIG. 1. The process steps described inFIGS. 30 through 51 may be applied using both n-type nano-FETs andp-type nano-FETs.

In FIG. 30, a second carrier substrate 160 is attached to a backsidesurface of a first IC die 200A (e.g., discussed above with respect toFIGS. 21A through 21C) using a first release layer 162 and a front-sideof a second IC die 200B (e.g., discussed above with respect to FIG. 21D)is bonded to a front-side of the first IC die 200A. The second carriersubstrate 160 may be a glass carrier substrate, a ceramic carriersubstrate, or the like. The second carrier substrate 160 may be a wafer,such that multiple first IC dies 200A and second IC dies 200B may beprocessed on the second carrier substrate 160 simultaneously.

The first release layer 162 may be formed of a polymer-based material,which may be subsequently removed along with the second carriersubstrate 160 from the overlying first IC die 200A. In some embodiments,the first release layer 162 is an epoxy-based thermal-release material,which loses its adhesive property when heated, such as alight-to-heat-conversion (LTHC) release coating. In other embodiments,the first release layer 162 may be an ultra-violet (UV) glue, whichloses its adhesive property when exposed to UV lights. The first releaselayer 162 may be dispensed as a liquid and cured, may be a laminate filmlaminated onto the second carrier substrate 160, or may be the like. Thetop surface of the first release layer 162 may be leveled and may have ahigh degree of planarity.

The second IC die 200B is then bonded to the first IC die 200A. Thesecond IC die 200B is face-to-face bonded to the first IC die 200A. Forexample, as illustrated in FIG. 30, the front-side interconnectstructure 120 of the second IC die 200B is directly bonded in aface-to-face manner by hybrid bonding to the front-side interconnectstructure 120 of the first IC die 200A. Specifically,dielectric-to-dielectric bonds are formed between a first dielectriclayer 124 of the first IC die 200A and a first dielectric layer 124 ofthe second IC die 200B and metal-to-metal bonds are formed between firstconductive features 122 of the first IC die 200A and first conductivefeatures 122 of the second IC die 200B.

As an example, a hybrid bonding process starts applying a surfacetreatment to the first dielectric layer 124 of the first IC die 200Aand/or the first dielectric layer 124 of the second IC die 200B. Thesurface treatment may include a plasma treatment. The plasma treatmentmay be performed in a vacuum environment. After the plasma treatment,the surface treatment may further include a cleaning process (e.g., arinse with deionized water or the like) that may be applied to the firstdielectric layer 124 of the first IC die 200A and/or the firstdielectric layer 124 of the second IC die 200B. The hybrid bondingprocess may then proceed to aligning the first conductive features 122of the second IC die 200B with the first conductive features 122 of thefirst IC die 200A. When the second IC die 200B is aligned with the firstIC die 200A, the first conductive features 122 of the second IC die 200Bmay overlap with the corresponding first conductive features 122 of thefirst IC die 200A. Next, the hybrid bonding includes a pre-bonding step,during which the second IC die 200B put in contact with the first IC die200A. The pre-bonding may be performed at room temperature (e.g.,between about 21° C. and about 25° C.). The hybrid bonding processcontinues with performing an anneal, for example, at a temperaturebetween about 150° C. and about 400° C. for a duration between about 0.5hours and about 3 hours, so that the metal in of the first conductivefeatures 122 of the second IC die 200B (e.g., copper) and the metal ofthe first conductive features 122 of the first IC die 200A (e.g.,copper) inter-diffuses, and the direct metal-to-metal bonds are formed.Although a single second IC die 200B is illustrated as being bonded tothe first IC die 200A, other embodiments may include multiple second ICdies 200B, which may be bonded to one or more first IC dies 200A. Insuch embodiments, the multiple second IC dies 200B and/or the multiplefirst IC dies 200A may be in a stacked configuration (e.g., havingmultiple stacked dies) and/or a side-by-side configuration.

The first IC die 200A and the second IC die 200B may be logic dies(e.g., central processing units (CPUs), graphics processing units(GPUs), system-on-a-chips (SoCs), application processors (APs),field-programmable gate arrays (FPGAs), microcontrollers, or the like),memory dies (e.g., dynamic random access memory (DRAM) dies, staticrandom access memory (SRAM) dies, or the like), power management dies(e.g., power management integrated circuit (PMIC) dies), radio frequency(RF) dies, sensor dies, micro-electro-mechanical-system (MEMS) dies,signal processing dies (e.g., digital signal processing (DSP) dies),front-end dies (e.g., analog front-end (AFE) dies), the like, orcombinations thereof.

In FIG. 31, a thinning process is applied to the backside of thesubstrate 50 of the second IC die 200B and a backside interconnectstructure 136, a passivation layer 144, UBMs 146, and externalconnectors 148 are formed over backsides of the substrate 50 and theepitaxial source/drain regions 92 of the second IC die 200B. Thesubstrate 50 may be thinned using processes the same as or similar tothose described above with respect to FIGS. 23A through 23C. Thebackside interconnect structure 136, the passivation layer 144, the UBMs146, and the external connectors 148 may be formed of materials andusing processes the same as or similar to those discussed above withrespect to FIGS. 24A through 29C.

In FIG. 32, a carrier substrate debonding is performed to detach (or“debond”) the second carrier substrate 160 from the first IC die 200Aand a first packaged semiconductor device 300A is formed. In someembodiments, the debonding includes projecting a light such as a laserlight or a UV light onto the first release layer 162 so that the firstrelease layer 162 decomposes under the heat of the light and the secondcarrier substrate 160 can be removed. Removing the second carriersubstrate 160 exposes the substrate 50 on the backside of the first ICdie 200A.

Conventional processes may form through substrate vias throughsubstrates in order to provide backside connections to integratedcircuit dies. In contrast, forming the second conductive lines 134(e.g., the power rails) and the backside interconnect structures 136 toprovide backside connections for the first packaged semiconductor device300A reduces the area required for backside connections, increasingdevice density, and improves the flexibility of backside connections.Moreover, bonding the second IC die 200B to the first IC die 200A usinghybrid bonding shortens the routing distance between the second IC die200B and the first IC die 200A and reduces the resistance between thesecond IC die 200B and the first IC die 200A. As such, the firstpackaged semiconductor device 300A may be formed with greater devicedensities, greater flexibility, and improved performance.

FIG. 33 illustrates a third IC die 200C, which may be used in packagedsemiconductor devices. The third IC die 200C may be formed by performingthe processes described above with respect to FIGS. 2 through 17C toform transistor structures 109, then performing the processes describedabove with respect to FIGS. 22A through 28C to form a backsideinterconnect structure 136. The processes described above with respectto FIGS. 18A through 23C (e.g., the processes used to form source/draincontacts 112, gate contacts 114, and a front-side interconnect structure120) may be skipped to form the third IC die 200C. A dicing process,such as sawing, a laser ablation method, an etching process, acombination thereof, or the like, may then be used to form the third ICdie 200C. The third IC die 200C may be a logic die (e.g., a centralprocessing unit (CPU), a graphics processing unit (GPU), asystem-on-a-chip (SoC), an application processor (AP), afield-programmable gate array (FPGA), a microcontroller, or the like), amemory die (e.g., a dynamic random access memory (DRAM) die, a staticrandom access memory (SRAM) die, or the like), a power management die(e.g., a power management integrated circuit (PMIC) die), a radiofrequency (RF) die, a sensor die, a micro-electro-mechanical-system(MEMS) die, a signal processing die (e.g., a digital signal processing(DSP) die), a front-end die (e.g., an analog front-end (AFE) die), thelike, or a combination thereof.

In FIG. 34, a second carrier substrate 160 is attached to a backsidesurface of a second IC die 200B (discussed above with respect to FIG.21D) using a first release layer 162 and a backside of a third IC die200C (discussed above with respect to FIG. 33) is bonded to a front-sideof the second IC die 200B. The second carrier substrate 160 may be aglass carrier substrate, a ceramic carrier substrate, or the like. Thesecond carrier substrate 160 may be a wafer, such that multiple secondIC dies 200B and third IC dies 200C may be processed on the secondcarrier substrate 160 simultaneously.

The first release layer 162 may be formed of a polymer-based material,which may be subsequently removed along with the second carriersubstrate 160 from the overlying second IC die 200B. In someembodiments, the first release layer 162 is an epoxy-basedthermal-release material, which loses its adhesive property when heated,such as a light-to-heat-conversion (LTHC) release coating. In otherembodiments, the first release layer 162 may be an ultra-violet (UV)glue, which loses its adhesive property when exposed to UV lights. Thefirst release layer 162 may be dispensed as a liquid and cured, may be alaminate film laminated onto the second carrier substrate 160, or may bethe like. The top surface of the first release layer 162 may be leveledand may have a high degree of planarity.

The third IC die 200C is then bonded to the second IC die 200B. Thethird IC die 200C is back-to-face bonded to the second IC die 200B. Forexample, as illustrated in FIG. 34, the backside interconnect structure136 of the third IC die 200C is directly bonded in a back-to-face mannerby hybrid bonding to the front-side interconnect structure 120 of thesecond IC die 200B. Specifically, dielectric-to-dielectric bonds areformed between a first dielectric layer 124 of the second IC die 200Band a fifth dielectric layer 138 of the third IC die 200C andmetal-to-metal bonds are formed between first conductive features 122 ofthe second IC die 200B and second conductive features 140 of the thirdIC die 200C.

In FIG. 35, source/drain contacts 112, gate contacts 114, a second ILD106, a front-side interconnect structure 120, a passivation layer 154,UBMs 156, and external connectors 158 are formed over a front-side ofthe third IC die 200C. The source/drain contacts 112, the gate contacts114, the second ILD 106, and the front-side interconnect structure 120may be formed of materials and using processes the same as or similar tothose discussed above with respect to FIGS. 18A through 21C.

The passivation layer 154, the UBMs 156, and the external connectors 158are then formed over the front-side interconnect structure 120. Thepassivation layer 154 may comprise polymers such as PBO, polyimide, BCB,or the like. Alternatively, the passivation layer 154 may includenon-organic dielectric materials such as silicon oxide, silicon nitride,silicon carbide, silicon oxynitride, or the like. The passivation layer154 may be deposited by, for example, CVD, PVD, ALD, or the like.

The UBMs 156 are formed through the passivation layer 154 to the firstconductive features 122 in the front-side interconnect structure 120 andthe external connectors 158 are formed on the UBMs 156. The UBMs 156 maycomprise one or more layers of copper, nickel, gold, or the like, whichare formed by a plating process, or the like. The external connectors158 (e.g., solder balls) are formed on the UBMs 156. The formation ofthe external connectors 158 may include placing solder balls on exposedportions of the UBMs 156 and reflowing the solder balls. In someembodiments, the formation of the external connectors 158 includesperforming a plating step to form solder regions over the topmost firstconductive features 122 and then reflowing the solder regions. The UBMs156 and the external connectors 158 may be used to provide input/outputconnections to other electrical components, such as, other device dies,redistribution structures, printed circuit boards (PCBs), motherboards,or the like. The UBMs 156 and the external connectors 158 may also bereferred to as front-side input/output pads that may provide signal,supply voltage, and/or ground connections to the nano-FETs of the thirdIC die 200C and the second IC die 200B.

In FIG. 36, a carrier substrate debonding is performed to detach (or“debond”) the second carrier substrate 160 from the second IC die 200Band a second packaged semiconductor device 300B is formed. In someembodiments, the debonding includes projecting a light such as a laserlight or a UV light onto the first release layer 162 so that the firstrelease layer 162 decomposes under the heat of the light and the secondcarrier substrate 160 can be removed. Removing the second carriersubstrate 160 exposes the substrate 50 on the backside of the second ICdie 200B.

Conventional processes may form through substrate vias throughsubstrates in order to provide backside connections to integratedcircuit dies. In contrast, forming the second conductive lines 134(e.g., the power rails) and the backside interconnect structures 136 toprovide backside connections for the second packaged semiconductordevice 300B reduces the area required for backside connections,increasing device density, and improves the flexibility of backsideconnections. Moreover, bonding the third IC die 200C to the second ICdie 200B using hybrid bonding shortens the routing distance between thethird IC die 200C and the second IC die 200B and reduces the resistancebetween the third IC die 200C and the second IC die 200B. As such, thesecond packaged semiconductor device 300B may be formed with greaterdevice densities, greater flexibility, and improved performance.

In FIG. 37, a second carrier substrate 160 is attached to a front-sidesurface of a third IC die 200Ci (discussed above with respect to FIG.33) using a first release layer 162 and a backside of a third IC die200Cii (discussed above with respect to FIG. 33) is bonded to a backsideof the third IC die 200Ci. The second carrier substrate 160 may be aglass carrier substrate, a ceramic carrier substrate, or the like. Thesecond carrier substrate 160 may be a wafer, such that multiple third ICdies 200Ci and third IC dies 200Cii may be processed on the secondcarrier substrate 160 simultaneously.

The first release layer 162 may be formed of a polymer-based material,which may be subsequently removed along with the second carriersubstrate 160 from the overlying third IC die 200Ci. In someembodiments, the first release layer 162 is an epoxy-basedthermal-release material, which loses its adhesive property when heated,such as a light-to-heat-conversion (LTHC) release coating. In otherembodiments, the first release layer 162 may be an ultra-violet (UV)glue, which loses its adhesive property when exposed to UV lights. Thefirst release layer 162 may be dispensed as a liquid and cured, may be alaminate film laminated onto the second carrier substrate 160, or may bethe like. The top surface of the first release layer 162 may be leveledand may have a high degree of planarity.

The third IC die 200Cii is then bonded to the third IC die 200Ci. Thethird IC die 200Cii is back-to-back bonded to the third IC die 200Ci.For example, as illustrated in FIG. 37, the backside interconnectstructure 136 of the third IC die 200Cii is directly bonded in aback-to-back manner by hybrid bonding to the backside interconnectstructure 136 of the third IC die 200Ci. Specifically,dielectric-to-dielectric bonds are formed between a fifth dielectriclayer 138 of the third IC die 200Ci and a fifth dielectric layer 138 ofthe third IC die 200Cii and metal-to-metal bonds are formed betweensecond conductive features 140 of the third IC die 200Ci and secondconductive features 140 of the third IC die 200Cii.

In FIG. 38, source/drain contacts 112, gate contacts 114, a second ILD106, a front-side interconnect structure 120, a passivation layer 154,UBMs 156, and external connectors 158 are formed over a front-side ofthe third IC die 200Cii. The source/drain contacts 112, the gatecontacts 114, the second ILD 106, and the front-side interconnectstructure 120 may be formed of materials and using processes the same asor similar to those discussed above with respect to FIGS. 18A through21C. Further, the passivation layer 154, the UBMs 156, and the externalconnectors 158 may be formed of materials and using processes the sameas or similar to those discussed above with respect to FIG. 35.

In FIG. 39, the structure of FIG. 38 is flipped such that a front-sideof the third IC die 200Ci faces upwards and a third carrier substrate170 is attached to a front-side of the front-side interconnect structure120 formed over the front-side of the third IC die 200Cii using a secondrelease layer 172. The third carrier substrate 170 may be a glasscarrier substrate, a ceramic carrier substrate, or the like. The thirdcarrier substrate 170 may be a wafer, such that multiple third IC dies200Ci and third IC dies 200Cii may be processed on third carriersubstrate 170 simultaneously.

The second release layer 172 may be formed of a polymer-based material,which may be subsequently removed along with the third carrier substrate170 from the overlying third IC die 200Cii. In some embodiments, thesecond release layer 172 is an epoxy-based thermal-release material,which loses its adhesive property when heated, such as alight-to-heat-conversion (LTHC) release coating. In other embodiments,the second release layer 172 may be an ultra-violet (UV) glue, whichloses its adhesive property when exposed to UV lights. The secondrelease layer 172 may be dispensed as a liquid and cured, may be alaminate film laminated onto the third carrier substrate 170, or may bethe like. The top surface of the second release layer 172 may be leveledand may have a high degree of planarity.

The third IC die 200Cii is then bonded to the third IC die 200Ci. Thethird IC die 200Cii is back-to-back bonded to the third IC die 200Ci.For example, as illustrated in FIG. 39, the backside interconnectstructure 136 of the third IC die 200Cii is directly bonded in aback-to-back manner by hybrid bonding to the backside interconnectstructure 136 of the third IC die 200Ci. Specifically,dielectric-to-dielectric bonds are formed between a fifth dielectriclayer 138 of the third IC die 200Ci and a fifth dielectric layer 138 ofthe third IC die 200Cii and metal-to-metal bonds are formed betweensecond conductive features 140 of the third IC die 200Ci and secondconductive features 140 of the third IC die 200Cii.

In FIG. 40, source/drain contacts 112, gate contacts 114, a second ILD106, a front-side interconnect structure 120, a passivation layer 154,UBMs 156, and external connectors 158 are formed over a front-side ofthe third IC die 200Ci. The source/drain contacts 112, the gate contacts114, the second ILD 106, and the front-side interconnect structure 120may be formed of materials and using processes the same as or similar tothose discussed above with respect to FIG. 38. Further, the passivationlayer 154, the UBMs 156, and the external connectors 158 may be formedof materials and using processes the same as or similar to thosediscussed above with respect to FIG. 38.

In FIG. 41, a carrier substrate debonding is performed to detach (or“debond”) the third carrier substrate 170 from the third IC die 200Ciiand a third packaged semiconductor device 300C is formed. In someembodiments, the debonding includes projecting a light such as a laserlight or a UV light onto the second release layer 172 so that the secondrelease layer 172 decomposes under the heat of the light and the thirdcarrier substrate 170 can be removed. Removing the third carriersubstrate 170 exposes the front-side interconnect structure 120 on thefront-side of the third IC die 200Cii.

Conventional processes may form through substrate vias throughsubstrates in order to provide backside connections to integratedcircuit dies. In contrast, forming the second conductive lines 134(e.g., the power rails) and the backside interconnect structures 136 toprovide backside connections for the third packaged semiconductor device300C reduces the area required for backside connections, increasingdevice density, and improves the flexibility of backside connections.Moreover, bonding the third IC die 200Cii to the third IC die 200Ciusing hybrid bonding shortens the routing distance between the third ICdie 200Cii and the third IC die 200Ci and reduces the resistance betweenthe third IC die 200Cii and the third IC die 200Ci. As such, the thirdpackaged semiconductor device 300C may be formed with greater devicedensities, greater flexibility, and improved performance.

In FIG. 42, a second carrier substrate 160 is attached to a backsidesurface of a first IC die 200Ai (discussed above with respect to FIGS.21A through 21C) using a first release layer 162 and a front-side of afirst IC die 200Aii (discussed above with respect to FIGS. 21A through21C) is bonded to a front-side of the first IC die 200Ai. The secondcarrier substrate 160 may be a glass carrier substrate, a ceramiccarrier substrate, or the like. The second carrier substrate 160 may bea wafer, such that multiple first IC dies 200Ai and first IC dies 200Aiimay be processed on the second carrier substrate 160 simultaneously.

The first release layer 162 may be formed of a polymer-based material,which may be subsequently removed along with the second carriersubstrate 160 from the overlying first IC die 200Ai. In someembodiments, the first release layer 162 is an epoxy-basedthermal-release material, which loses its adhesive property when heated,such as a light-to-heat-conversion (LTHC) release coating. In otherembodiments, the first release layer 162 may be an ultra-violet (UV)glue, which loses its adhesive property when exposed to UV lights. Thefirst release layer 162 may be dispensed as a liquid and cured, may be alaminate film laminated onto the second carrier substrate 160, or may bethe like. The top surface of the first release layer 162 may be leveledand may have a high degree of planarity.

The first IC die 200Aii is then bonded to the first IC die 200Ai. Thefirst IC die 200Aii is face-to-face bonded to the first IC die 200Ai.For example, as illustrated in FIG. 42, the front-side interconnectstructure 120 of the first IC die 200Aii is directly bonded in aface-to-face manner by hybrid bonding to the front-side interconnectstructure 120 of the first IC die 200Ai. Specifically,dielectric-to-dielectric bonds are formed between a first dielectriclayer 124 of the first IC die 200Ai and a first dielectric layer 124 ofthe first IC die 200Aii and metal-to-metal bonds are formed betweenfirst conductive features 122 of the first IC die 200Ai and firstconductive features 122 of the first IC die 200Ai.

In FIG. 43, a thinning process is applied to the backside of thesubstrate 50 of the first IC die 200Aii and a backside interconnectstructure 136 is formed over backsides of the substrate 50 and theepitaxial source/drain regions 92 of the first IC die 200Aii. Thesubstrate 50 may be thinned using processes the same as or similar tothose described above with respect to FIGS. 23A through 23C. Thebackside interconnect structure 136 may be formed of materials and usingprocesses the same as or similar to those discussed above with respectto FIGS. 24A through 28C.

In FIG. 44, the structure of FIG. 43 is flipped such that a backside ofthe first IC die 200Ai faces upwards and a third carrier substrate 170is attached to a backside of the backside interconnect structure 136formed over the backside of the first IC die 200Aii using a secondrelease layer 172. The third carrier substrate 170 may be a glasscarrier substrate, a ceramic carrier substrate, or the like. The thirdcarrier substrate 170 may be a wafer, such that multiple first IC dies200Ai and first IC dies 200Aii may be processed on third carriersubstrate 170 simultaneously.

The second release layer 172 may be formed of a polymer-based material,which may be subsequently removed along with the third carrier substrate170 from the overlying first IC die 200Aii. In some embodiments, thesecond release layer 172 is an epoxy-based thermal-release material,which loses its adhesive property when heated, such as alight-to-heat-conversion (LTHC) release coating. In other embodiments,the second release layer 172 may be an ultra-violet (UV) glue, whichloses its adhesive property when exposed to UV lights. The secondrelease layer 172 may be dispensed as a liquid and cured, may be alaminate film laminated onto the third carrier substrate 170, or may bethe like. The top surface of the second release layer 172 may be leveledand may have a high degree of planarity.

In FIG. 45, a thinning process is applied to the backside of thesubstrate 50 of the first IC die 200Ai and a backside interconnectstructure 136, a passivation layer 144, UBMs 146, and externalconnectors 148 are formed over backsides of the substrate 50 and theepitaxial source/drain regions 92 of the first IC die 200Ai. Thesubstrate 50 may be thinned using processes the same as or similar tothose described above with respect to FIGS. 23A through 23C. Thebackside interconnect structure 136, the passivation layer 144, the UBMs146, and the external connectors 148 may be formed of materials andusing processes the same as or similar to those discussed above withrespect to FIGS. 24A through 29C.

In FIG. 46, a carrier substrate debonding is performed to detach (or“debond”) the third carrier substrate 170 from the first IC die 200Aiiand a fourth packaged semiconductor device 300D is formed. In someembodiments, the debonding includes projecting a light such as a laserlight or a UV light onto the second release layer 172 so that the secondrelease layer 172 decomposes under the heat of the light and the thirdcarrier substrate 170 can be removed. Removing the third carriersubstrate 170 exposes the backside interconnect structure 136 on thebackside of the first IC die 200Aii.

Conventional processes may form through substrate vias throughsubstrates in order to provide backside connections to integratedcircuit dies. In contrast, forming the second conductive lines 134(e.g., the power rails) and the backside interconnect structures 136 toprovide backside connections for the fourth packaged semiconductordevice 300D reduces the area required for backside connections,increasing device density, and improves the flexibility of backsideconnections. Moreover, bonding the first IC die 200Aii to the first ICdie 200Ai using hybrid bonding shortens the routing distance between thefirst IC die 200Aii and the first IC die 200Ai and reduces theresistance between the first IC die 200Aii and the first IC die 200Ai.As such, the fourth packaged semiconductor device 300D may be formedwith greater device densities, greater flexibility, and improvedperformance.

In FIG. 47, a second carrier substrate 160 is attached to a backsidesurface of a first IC die 200A (discussed above with respect to FIGS.21A through 21C) using a first release layer 162 and a backside of athird IC die 200C (discussed above with respect to FIG. 33) is bonded toa front-side of the first IC die 200A. The second carrier substrate 160may be a glass carrier substrate, a ceramic carrier substrate, or thelike. The second carrier substrate 160 may be a wafer, such thatmultiple first IC dies 200A and third IC dies 200C may be processed onthe second carrier substrate 160 simultaneously.

The first release layer 162 may be formed of a polymer-based material,which may be subsequently removed along with the second carriersubstrate 160 from the overlying first IC die 200A. In some embodiments,the first release layer 162 is an epoxy-based thermal-release material,which loses its adhesive property when heated, such as alight-to-heat-conversion (LTHC) release coating. In other embodiments,the first release layer 162 may be an ultra-violet (UV) glue, whichloses its adhesive property when exposed to UV lights. The first releaselayer 162 may be dispensed as a liquid and cured, may be a laminate filmlaminated onto the second carrier substrate 160, or may be the like. Thetop surface of the first release layer 162 may be leveled and may have ahigh degree of planarity.

The third IC die 200C is then bonded to the first IC die 200A. The thirdIC die 200C is back-to-face bonded to the first IC die 200A. Forexample, as illustrated in FIG. 47, the backside interconnect structure136 of the third IC die 200C is directly bonded in a back-to-face mannerby hybrid bonding to the front-side interconnect structure 120 of thefirst IC die 200A. Specifically, dielectric-to-dielectric bonds areformed between a first dielectric layer 124 of the first IC die 200A anda fifth dielectric layer 138 of the third IC die 200C and metal-to-metalbonds are formed between first conductive features 122 of the first ICdie 200A and second conductive features 140 of the third IC die 200C.

In FIG. 48, source/drain contacts 112, gate contacts 114, a second ILD106, and a front-side interconnect structure 120 are formed over afront-side of the third IC die 200C. The source/drain contacts 112, thegate contacts 114, the second ILD 106, and the front-side interconnectstructure 120 may be formed of materials and using processes the same asor similar to those discussed above with respect to FIGS. 18A through21C.

In FIG. 49, the structure of FIG. 48 is flipped such that a backside ofthe first IC die 200A faces upwards and a third carrier substrate 170 isattached to a front-side of the front-side interconnect structure 120formed over the front-side of the third IC die 200C using a secondrelease layer 172. The third carrier substrate 170 may be a glasscarrier substrate, a ceramic carrier substrate, or the like. The thirdcarrier substrate 170 may be a wafer, such that multiple first IC dies200A and third IC dies 200C may be processed on third carrier substrate170 simultaneously.

The second release layer 172 may be formed of a polymer-based material,which may be subsequently removed along with the third carrier substrate170 from the overlying third IC die 200C. In some embodiments, thesecond release layer 172 is an epoxy-based thermal-release material,which loses its adhesive property when heated, such as alight-to-heat-conversion (LTHC) release coating. In other embodiments,the second release layer 172 may be an ultra-violet (UV) glue, whichloses its adhesive property when exposed to UV lights. The secondrelease layer 172 may be dispensed as a liquid and cured, may be alaminate film laminated onto the third carrier substrate 170, or may bethe like. The top surface of the second release layer 172 may be leveledand may have a high degree of planarity.

In FIG. 50, a thinning process is applied to the backside of thesubstrate 50 of the first IC die 200A and a backside interconnectstructure 136, a passivation layer 144, UBMs 146, and externalconnectors 148 are formed over backsides of the substrate 50 and theepitaxial source/drain regions 92 of the first IC die 200A. Thesubstrate 50 may be thinned using processes the same as or similar tothose described above with respect to FIGS. 23A through 23C. Thebackside interconnect structure 136, the passivation layer 144, the UBMs146, and the external connectors 148 may be formed of materials andusing processes the same as or similar to those discussed above withrespect to FIGS. 24A through 29C.

In FIG. 51, a carrier substrate debonding is performed to detach (or“debond”) the third carrier substrate 170 from the third IC die 200C anda fifth packaged semiconductor device 300E is formed. In someembodiments, the debonding includes projecting a light such as a laserlight or a UV light onto the second release layer 172 so that the secondrelease layer 172 decomposes under the heat of the light and the thirdcarrier substrate 170 can be removed. Removing the third carriersubstrate 170 exposes the front-side interconnect structure 120 on thefront-side of the third IC die 200C.

Conventional processes may form through substrate vias throughsubstrates in order to provide backside connections to integratedcircuit dies. In contrast, forming the second conductive lines 134(e.g., the power rails) and the backside interconnect structures 136 toprovide backside connections for the fifth packaged semiconductor device300E reduces the area required for backside connections, increasingdevice density, and improves the flexibility of backside connections.Moreover, bonding the third IC die 200C to the first IC die 200A usinghybrid bonding shortens the routing distance between the third IC die200C and the first IC die 200A and reduces the resistance between thethird IC die 200C and the first IC die 200A. As such, the fifth packagedsemiconductor device 300E may be formed with greater device densities,greater flexibility, and improved performance.

Embodiments may achieve advantages. For example, forming IC dies whichinclude backside interconnect structures and including backside powerrails in the backside interconnect structures reduces interconnect area,shortens routing distance, increasing the flexibility of interconnectarea layouts, and increases device density. Moreover, using hybridbonding between IC dies in packaged semiconductor devices further aidsin increasing the flexibility of interconnect area layouts and shortensrouting distance, which improves device performance.

In accordance with an embodiment, a device includes a first integratedcircuit device including a first transistor structure in a first devicelayer; a front-side interconnect structure on a front-side of the firstdevice layer; and a backside interconnect structure on a backside of thefirst device layer, the backside interconnect structure including afirst dielectric layer on the backside of the first device layer; and afirst contact extending through the first dielectric layer to asource/drain region of the first transistor structure; and a secondintegrated circuit device including a second transistor structure in asecond device layer; and a first interconnect structure on the seconddevice layer, the first interconnect structure being bonded to thefront-side interconnect structure by dielectric-to-dielectric andmetal-to-metal bonds. In an embodiment, the first interconnect structureis disposed on a front-side of the second device layer. In anembodiment, the first interconnect structure includes a front-side powerrail, and the backside interconnect structure includes a backside powerrail electrically coupled to the source/drain region of the firsttransistor structure through the first contact. In an embodiment, thesecond integrated circuit device further includes a second interconnectstructure disposed on a backside of the second device layer, the secondinterconnect structure including a second dielectric layer on thebackside of the second device layer; and a second contact extendingthrough the second dielectric layer to a source/drain region of thesecond transistor structure. In an embodiment, the backside interconnectstructure includes a first backside power rail electrically coupled tothe source/drain region of the first transistor structure through thefirst contact, and the second interconnect structure includes a secondbackside power rail electrically coupled to the source/drain region ofthe second transistor structure through the second contact. In anembodiment, the first interconnect structure is disposed on a backsideof the second device layer. In an embodiment, the first interconnectstructure includes a second dielectric layer on a backside of the seconddevice layer; and a second contact extending through the seconddielectric layer to a source/drain region of the second transistorstructure. In an embodiment, the backside interconnect structureincludes a first backside power rail electrically coupled to thesource/drain region of the first transistor structure through the firstcontact, and the first interconnect structure includes a second backsidepower rail electrically coupled to the source/drain region of the secondtransistor structure through the second contact.

In accordance with another embodiment, a device includes a firstintegrated circuit device including a first substrate; a first devicelayer over the first substrate, the first device layer including a firsttransistor structure; and a first interconnect structure over the firstdevice layer, the first interconnect structure including a first powerrail on a backside of the first device layer, the first power rail beingelectrically coupled to a first source/drain region of the firsttransistor structure through a first backside via; and a secondintegrated circuit device including a second substrate; a second devicelayer over the second substrate, the second device layer including asecond transistor structure; and a second interconnect structure overthe second device layer, the second interconnect structure being bondedto the first interconnect structure by dielectric-to-dielectric andmetal-to-metal bonds. In an embodiment, the backside via is electricallycoupled to the first source/drain region through a first silicideregion. In an embodiment, the second interconnect structure includes asecond dielectric layer over a backside of the second device layer; anda second power rail over the second dielectric layer, the second powerrail being electrically coupled to a second source/drain region of thesecond transistor structure through a second backside via. In anembodiment, the second interconnect structure is on a front-side of thesecond device layer, the second integrated circuit device furtherincludes a third interconnect structure over the second device layer,the third interconnect structure including a second power rail on abackside of the second device layer, the second power rail beingelectrically coupled to a second source/drain region of the secondtransistor structure through a second backside via. In an embodiment,the second integrated circuit device further includes a passivationlayer on a surface of the third interconnect structure opposite thesecond device layer; an underbump metallization (UBM) in the passivationlayer; and an external connector on the UBM, the external connectorbeing electrically coupled to the third interconnect structure throughthe UBM. In an embodiment, the second integrated circuit device includesa gate contact electrically coupled to a gate structure of the secondtransistor structure, the second interconnect structure including asecond power rail over a front-side of the second device layer, thesecond power rail being electrically coupled to the gate structurethrough the gate contact.

In accordance with yet another embodiment, a method includes forming afirst transistor on a first substrate; forming a first interconnectstructure over the first transistor; exposing a first source/drainregion of the first transistor, exposing the first source/drain regionincluding thinning the first substrate; after exposing the firstsource/drain region, forming a second interconnect structure over thefirst transistor opposite the first interconnect structure, forming thesecond interconnect structure including depositing a first dielectriclayer over the first transistor; forming a first backside via throughthe first dielectric layer and electrically coupled to a firstsource/drain region of the first transistor; and forming a firstconductive line electrically connected to the first backside via; andbonding a first integrated circuit device to the first interconnectstructure, bonding the first integrated circuit device to the firstinterconnect structure including forming dielectric-to-dielectric bondsbetween the first integrated circuit device and the first interconnectstructure. In an embodiment, the method further includes forming thefirst integrated circuit device, forming the first integrated circuitdevice including forming a second transistor on a second substrate; andforming a third interconnect structure over the second transistoropposite the second substrate, bonding the first integrated circuitdevice to the first interconnect structure including forming thedielectric-to-dielectric bonds between the third interconnect structureand the first interconnect structure. In an embodiment, forming thethird interconnect structure includes forming a second conductive lineover and electrically coupled to the second transistor, the firstconductive line being a first power rail, and the second conductive linebeing a second power rail. In an embodiment, the method further includesforming the first integrated circuit device, forming the firstintegrated circuit device including forming a second transistor on asecond substrate; exposing a second source/drain region of the secondtransistor, exposing the second source/drain region including thinningthe second substrate; and after exposing the second source/drain region,forming a third interconnect structure over the second transistor,forming the third interconnect structure including depositing a seconddielectric layer over the second transistor; forming a second backsidevia through the second dielectric layer and electrically coupled to asecond source/drain region of the second transistor; and forming asecond conductive line electrically connected to the second backsidevia. In an embodiment, bonding the first integrated circuit device tothe first interconnect structure includes forming thedielectric-to-dielectric bonds between third interconnect structure andthe first interconnect structure. In an embodiment, forming the firstintegrated circuit device further includes forming a fourth interconnectstructure over the second transistor opposite the third interconnectstructure, bonding the first integrated circuit device to the firstinterconnect structure including forming the dielectric-to-dielectricbonds between the fourth interconnect structure and the firstinterconnect structure.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device comprising: a first integrated circuit device comprising: a first transistor structure in a first device layer; a front-side interconnect structure on a front-side of the first device layer; and a backside interconnect structure on a backside of the first device layer, the backside interconnect structure comprising: a first dielectric layer on the backside of the first device layer; and a first contact extending through the first dielectric layer to a source/drain region of the first transistor structure; and a second integrated circuit device comprising: a second transistor structure in a second device layer; and a first interconnect structure on the second device layer, wherein the first interconnect structure is bonded to the front-side interconnect structure by dielectric-to-dielectric and metal-to-metal bonds.
 2. The device of claim 1, wherein the first interconnect structure is disposed on a front-side of the second device layer.
 3. The device of claim 2, wherein the first interconnect structure comprises a front-side power rail, and wherein the backside interconnect structure comprises a backside power rail electrically coupled to the source/drain region of the first transistor structure through the first contact.
 4. The device of claim 2, wherein the second integrated circuit device further comprises a second interconnect structure disposed on a backside of the second device layer, the second interconnect structure comprising: a second dielectric layer on the backside of the second device layer; and a second contact extending through the second dielectric layer to a source/drain region of the second transistor structure.
 5. The device of claim 4, wherein the backside interconnect structure comprises a first backside power rail electrically coupled to the source/drain region of the first transistor structure through the first contact, and wherein the second interconnect structure comprises a second backside power rail electrically coupled to the source/drain region of the second transistor structure through the second contact.
 6. The device of claim 1, wherein the first interconnect structure is disposed on a backside of the second device layer.
 7. The device of claim 6, wherein the first interconnect structure comprises: a second dielectric layer on a backside of the second device layer; and a second contact extending through the second dielectric layer to a source/drain region of the second transistor structure.
 8. The device of claim 7, wherein the backside interconnect structure comprises a first backside power rail electrically coupled to the source/drain region of the first transistor structure through the first contact, and wherein the first interconnect structure comprises a second backside power rail electrically coupled to the source/drain region of the second transistor structure through the second contact.
 9. A device comprising: a first integrated circuit device comprising: a first substrate; a first device layer over the first substrate, the first device layer comprising a first transistor structure; and a first interconnect structure over the first device layer, the first interconnect structure comprising a first power rail on a backside of the first device layer, the first power rail being electrically coupled to a first source/drain region of the first transistor structure through a first backside via; and a second integrated circuit device comprising: a second substrate; a second device layer over the second substrate, the second device layer comprising a second transistor structure; and a second interconnect structure over the second device layer, wherein the second interconnect structure is bonded to the first interconnect structure by dielectric-to-dielectric and metal-to-metal bonds.
 10. The device of claim 9, wherein the first backside via is electrically coupled to the first source/drain region through a first silicide region.
 11. The device of claim 9, wherein the second interconnect structure comprises: a second dielectric layer over a backside of the second device layer; and a second power rail over the second dielectric layer, the second power rail being electrically coupled to a second source/drain region of the second transistor structure through a second backside via.
 12. The device of claim 9, wherein the second interconnect structure is on a front-side of the second device layer, wherein the second integrated circuit device further comprises a third interconnect structure over the second device layer, the third interconnect structure comprising a second power rail on a backside of the second device layer, the second power rail being electrically coupled to a second source/drain region of the second transistor structure through a second backside via.
 13. The device of claim 12, wherein the second integrated circuit device further comprises: a passivation layer on a surface of the third interconnect structure opposite the second device layer; an underbump metallization (UBM) in the passivation layer; and an external connector on the UBM, the external connector being electrically coupled to the third interconnect structure through the UBM.
 14. The device of claim 9, wherein the second integrated circuit device comprises a gate contact electrically coupled to a gate structure of the second transistor structure, wherein the second interconnect structure comprises a second power rail over a front-side of the second device layer, the second power rail being electrically coupled to the gate structure through the gate contact.
 15. A method comprising: forming a first transistor on a first substrate; forming a first interconnect structure over the first transistor; exposing a first source/drain region of the first transistor, wherein exposing the first source/drain region comprises thinning the first substrate; after exposing the first source/drain region, forming a second interconnect structure over the first transistor opposite the first interconnect structure, wherein forming the second interconnect structure comprises: depositing a first dielectric layer over the first transistor; forming a first backside via through the first dielectric layer and electrically coupled to a first source/drain region of the first transistor; and forming a first conductive line electrically connected to the first backside via; and bonding a first integrated circuit device to the first interconnect structure, wherein bonding the first integrated circuit device to the first interconnect structure comprises forming dielectric-to-dielectric bonds between the first integrated circuit device and the first interconnect structure.
 16. The method of claim 15, further comprising forming the first integrated circuit device, wherein forming the first integrated circuit device comprises: forming a second transistor on a second substrate; and forming a third interconnect structure over the second transistor opposite the second substrate, wherein bonding the first integrated circuit device to the first interconnect structure comprises forming the dielectric-to-dielectric bonds between the third interconnect structure and the first interconnect structure.
 17. The method of claim 16, wherein forming the third interconnect structure comprises forming a second conductive line over and electrically coupled to the second transistor, wherein the first conductive line is a first power rail, and wherein the second conductive line is a second power rail.
 18. The method of claim 15, further comprising forming the first integrated circuit device, wherein forming the first integrated circuit device comprises: forming a second transistor on a second substrate; exposing a second source/drain region of the second transistor, wherein exposing the second source/drain region comprises thinning the second substrate; and after exposing the second source/drain region, forming a third interconnect structure over the second transistor, wherein forming the third interconnect structure comprises: depositing a second dielectric layer over the second transistor; forming a second backside via through the second dielectric layer and electrically coupled to a second source/drain region of the second transistor; and forming a second conductive line electrically connected to the second backside via.
 19. The method of claim 18, wherein bonding the first integrated circuit device to the first interconnect structure comprises forming the dielectric-to-dielectric bonds between the third interconnect structure and the first interconnect structure.
 20. The method of claim 18, wherein forming the first integrated circuit device further comprises forming a fourth interconnect structure over the second transistor opposite the third interconnect structure, wherein bonding the first integrated circuit device to the first interconnect structure comprises forming the dielectric-to-dielectric bonds between the fourth interconnect structure and the first interconnect structure. 